OPINION
AMUNDSON, Judge.After third parties entered an apartment and killed a tenant, the tenant’s wrongful death trustee sued the landlord, alleging the landlord’s negligence contributed to the tenant’s death. The landlord moved for summary judgment, and the district court granted the motion. Tenant’s trustee appeals, alleging that (a) a Minneapolis housing ordinance required the landlord to repair the door to the apartment; (b) regardless of the duty imposed by the Minneapolis Housing ordinance, the landlord had an independent duty to make sure that the apartment was secure; and (c) the lease required the landlord to repair the door.
FACTS
On May 12, 1995, J.W. Haynes was murdered in his apartment. Intruders gained access to the apartment building without using force and subsequently entered the apartment he shared with his girlfriend and their son. Haynes’ mother, appellant Janice Funchess, commenced a wrongful-death action against respondent Cecil Newman Corporation (Newman), owner of Haynes’ apartment building. Funchess alleged that the assailants were able to gain entrance to the building through a security door that had a broken lock. The district court granted summary judgment, finding that Newman owed no duty to Haynes. This appeal followed.
ISSUES
I. Was respondent obligated to protect decedent from the criminal acts of third parties?
II. Did respondent owe the decedent a statutory duty of care to maintain door locks in working condition? If so, were sufficient questions of material fact raised, rendering the district court’s grant of summary judgment erroneous?
III. Is the intervening cause of a criminal act sufficiently foreseeable, so as to maintain the chain of causation?
IV. Did respondent have a contractual duty to maintain the door locks in working condition?
V. Should appellant’s motion to strike portions of respondent’s brief be granted?
ANALYSIS
Summary judgment may be granted when there is no genuine issue of *400material fact and either party is entitled to judgment as a matter of law. Minn. R. Civ. P. 56.03. To prevail on a negligence claim, a plaintiff must show: (1) the existence of a duty; (2) breach of that duty; (3) that the breach proximately caused the injury; and (4) injury in fact. Hudson v. Snyder Body, Inc., 326 N.W.2d 149, 157 (Minn.1982). The existence of a legal duty may be imposed by either the common law or a statute, Steffey v. Soo Line R.R., 498 N.W.2d 304, 307 (Minn.App.1993), review denied (Minn. May 28, 1993), and is a question of law for the court to determine. Larson v. Larson, 373 N.W.2d 287, 289 (Minn.1985). But the determination of .whether a duty has been breached is generally within the province of the jury. Smith v. Carriere, 316 N.W.2d 574, 575 (Minn.1982).
I. Common Law Duty and Special Relationship Exception
This appeal centers on what duty, if any, Newman owed Haynes. The district court granted summary judgment because it determined that Newman had no duty to protect Haynes. Specifically, the court concluded that no special relationship existed between Newman and Haynes that would give rise to a duty to protect.
Holding a landlord liable for the intentional criminal acts of a third party is a modern development, representing , a change from the common law. See Errico v. Southland Corp., 509 N.W.2d 585, 587 (Minn.App.1993) (generally, a person “has no duty to control the conduct of a third person in order to prevent that person from causing injury to another”), review denied (Minn. Jan. 27, 1994); see also Donaldson v. Young Women’s Christian Ass’n, 539 N.W.2d 789, 792 (Minn.1995) (a person generally has no duty to act for the protection of another, even if he or she realizes or should realize that action is necessary).
A landlord-tenant relationship, standing alone, is not sufficient to give rise to the duty to protect. See Spitzak v. Hylands, Ltd., 500 N.W.2d 154, 156-57 (Minn.App.1993) (failing to find landlord liable where apartment complex neither exposed tenants to greater risks, nor presented a unique opportunity for criminals and criminal activity), review denied (Minn. July 15, 1993).1 But a party may owe such a duty where a special relationship exists between that party and another that gives the other the right to protection. Errico, 509 N.W.2d at 587. When a special relationship exists, a party has the duty to take reasonable precautions against foreseeable criminal acts of third parties. Id. The rationale running through special relationships is that one party relinquishes part of its autonomy, or the ability to control the environment, in favor of another, usually dominant, party. See id. (special relationships exist when one entrusts her safety to another and the other accepts that entrustment). The imposition of liability on the dominant party not only redresses the imbalance of power, but places the precautionary burden more directly on such party. Id.
Historically, this principle did not apply to a typical landlord-tenant relationship. In pre-industrial-age leases, tenants did not usually relinquish their autonomy or their ability to control their surroundings. A typical tenant had full control over the land, including its own actions on the land. *401Thus, these relationships were properly excluded from the special relationships. Changes in society have caused modern leases to differ materially from those in the past. The hotel-and-guest relationship was one of the first to be considered special. Courts extended the special relationship to hotels because the reasons for the rule were acutely present; guests had no autonomy or ability to control their surroundings. Likewise, tenants in apartment buildings, whose'leases are often of short duration, cannot be expected to secure common areas of the building by individually making the necessary expenditures, for example, to install and maintain locks on outside entrances. See Tedder v. Raskin, 728 S.W.2d 343, 348 (Tenn.App.1987) (landlord may be liable for injuries to tenants from third-party crimes on the premises because landlord is in far superi- or position to take necessary steps to secure premises).
When Haynes signed the lease, he relinquished to Newman exclusive control over building security, the building’s security devices, and the areas outside his apartment unit. These factors are sufficient to create the existence of a special relationship as the logical extrapolation of the existing common law governing the special-relationship between innkeeper and guest. See generally Boone v. Martinez, 567 N.W.2d 508, 510 (Minn.1997) (discussing innkeeper liability in the context of a tavern’s duty to maintain safety and order for protection of its patrons). Because the special relationship exception applies, Newman had the duty to use reasonable care to prevent foreseeable criminal acts of third parties. Newman may have breached this duty if it took no action to remedy the defective lock, a genuine issue of a material fact.
But even if Newman had no duty to protect Haynes by providing reasonable security measures, it did have a duty to maintain the security measures already undertaken for the protection of its tenants. Specifically, by providing a secured back door to the building, Newman assumed the duty to maintain the locking mechanism on that door. See Cracraft v. City of St. Louis Park, 279 N.W.2d 801, 806 (Minn.1979) (finding municipality’s duty of care with regard to fire code violations when municipality assumes to act for the protection of others, as distinguished from acting merely for itself when it inspects property for fire-code violations); see also State by Humphrey v. Philip Morris, Inc., 551 N.W.2d 490, 493 (Minn.1996) (“[Ojne who assumes to act, even though gratuitously, may thereby become subject to the duty of acting carefully, if he acts at all.”).
Where a person or entity voluntarily assumes a duty, then that duty must be exercised with reasonable care and the failure to so act may result in liability. Nickelson v. Mall of Am. Co., 593 N.W.2d 723, 726 (Minn.App.1999). We conclude that Newman had a duty to maintain the security locking mechanism on the apartment building’s back door. The parties dispute whether, in fact, the locking mechanism was working properly at the time of Haynes’ murder. This, of course, is another unresolved genuine issue of material fact. Not recognizing this, the district court again erred in granting summary judgment to Newman.
II. Statutory Duty
Funchess also, argues that Newman’s duty arose by statute. The difference between a statutorily imposed duty and a duty arising under common law is that the duty imposed by statute is fixed. Zerby v. Warren, 297 Minn. 134, 139, 210 N.W.2d 58, 62 (1973). If an ordinance imposes a duty and one neglects to perform that duty, then he or she is “liable to those for whose protection the statute was enacted for any damages resulting proximately from such * * * neglect.” Henderson v. Bjork Monument Co., 222 Minn. 241, 245, 24 N.W.2d 42, 45 (1946) (citation omitted). A breach of this nature *402generally constitutes conclusive evidence of negligence, or negligence per se. Zerby, 297 Minn. at 139, 210 N.W.2d at 62. Minneapolis, Minn., Code of Ordinances § 244.675 (1998), requires that all doorways leading to the exterior or entry of a multiple dwelling, such as the apartment building in question, “be secured by a locking device * * * that will engage and lock automatically when the door is in the closed position within the frame provided.” The ordinance also mandates that “[a]ll locking devices required by this section shall be kept in a professional state of maintenance and repair.” Id.
The parties dispute whether the locking mechanism on the back door was broken. Funchess presented the affidavit of Angela Bennett, who stated that on the day of the murder, she was able to enter the apartment through the back door without using a key, although nothing was propping the door open and no one opened the door for her. Newman, on the other hand, introduced an affidavit from Randy Gott, stating that tenants often thwarted the locking mechanism on the back door by propping the door open. Additionally, Gott’s affidavit asserted it was not uncommon for people to be buzzed into the building by other tenants.
Considering the ordinance-im--posed duty to maintain the locking mechanism on the back door, the district court’s grant of summary judgment was premature. Determinations regarding breach and causation — that is, whether the lock in this case was actually broken- — generally present questions of fact properly determined by a jury. See Smith, 316 N.W.2d at 575 (breach); Lubbers v. Anderson, 539 N.W.2d 398, 402 (Minn.1995) (causation). When reasonable minds could reach only one conclusion, the existence of proximate cause is, of course, a question of law. Lubbers, 539 N.W.2d at 402. But there must also be a showing that the defendant’s conduct “was a substantial factor in bringing about the injury.” Flom v. Flom, 291 N.W.2d 914, 917 (Minn.1980).
Here, Newman owed a duty to Haynes to keep the back-door lock working properly. Assuming, for purposes of this appeal, that Newman breached this duty by allowing the back-door lock to remain in a state of disrepair, it cannot be said that Newman would have no reason to anticipate that breach of this duty would result in injury to its tenants. The parties disagree whether the alleged breach of this duty was a substantial factor in bringing about Haynes’ death, or whether Haynes himself was responsible by allowing his assailants access into the building. More than one conclusion as to the causes of Haynes’ death can be reached, and because reasonable minds could differ on the issue of causation, summary judgment in-favor of Newman should not have been granted.
III. Intervening Cause
A theoretical problem results when the actual harm is caused by a force other than tfyat initiated by the negligent actor. These forces may supercede the original actor’s liability. See Pearson v. Henkemeyer, 503 N.W.2d 504, 507 (Minn.App.1993) (generally, a third party’s criminal act “breaks the causation chain” unless the criminal act “is reasonably foreseeable”), review denied (Minn. Sept. 30, 1993). An intervening cause is one that comes about after the negligent act. It must come between the negligent act of the actor and the resulting harm, shifting the responsibility for the harm to the intervening act. If the actual harm is caused by an intervening act, the negligent actor is absolved from liability. See Restatement (Second) of Torts § 448 (1965).
But where the occurrence of the intervening act is reasonably foreseeable, the chain of causation will not be broken. Id. In this ease, the assault is entirely foreseeable under the totality of the circumstances. A lock is intended to prevent crimes against people and property within the area it secures. If the lock is *403ineffective, a crime is a foreseeable result. This is especially the case where, as here, the building is located in an area notorious for criminal activity. When a landlord beaches-his duty to maintain a lock, the landlord may be held hable for the foreseeable result — in this case, a violent assault resulting in death.
IV. Lease As Contract
A lease is one form of contract. Minneapolis Pub. Hous. Auth. v. Lor, 591 N.W.2d 700, 704 (Minn.1999). As such, the parties can insert almost any provision they choose. Here, the lease required the landlord to “maintain the common areas and facilities in safe condition * * * [and] make necessary repairs with reasonable promptness.” Where contract language is unambiguous, we will give it its plain and ordinary meaning. Bob Useldinger & Sons, Inc. v. Hangsleben, 505 N.W.2d 323, 328 (Minn.1993). A reasonable construction of the lease requires Newman to maintain the locks on the building doors in working condition and to repair them promptly if they are not locking properly. A question of fact exists as to whether Newman breached its contractual duty to keep the back-door lock in working condition. Thus, the district court’s grant of summary judgment to Newman was premature.
V. Motion to Strike
Appellant requests that this court strike portions of respondent’s brief that rely on alleged hearsay statements given by Newman’s security guard. See Walker v. Wayne County, Iowa, 850 F.2d 433, 434 (8th Cir.1988) (in a summary judgment proceeding, only evidence admissible or usable at trial should be considered). But we need not consider the security guard’s reports of alleged comments made by residents of the apartment in determining whether sufficient facts are in dispute to render summary judgment improper. Because we find the objected-to portions of Newman’s brief irrelevant to our decision, we deny appellant’s motion to strike.
DECISION
Newman owed the decedent a common-law- duty, a statutory duty, and a contractual duty to maintain the security locking mechanism on the back door of the apartment building in working condition. These duties were not abrogated by the foreseeable criminal acts of a third party. Because genuine issues of material fact exists with, regard to the security door’s condition and causation, we reverse the district court’s grant of summary judgment and remand for further proceedings.
Reversed and remanded; motion denied.
. Liability can be imposed on landlords for the criminal acts of third parties in certain situations. See Erickson v. Curtis Inv. Co., 447 N.W.2d 165, 168-69 (Minn.1989) (under the special relationship doctrine, owner and operator of commercial parking ramp facility owed a duty to provide adequate security to its customers to deter criminal activity in the parking ramp); Ponticas v. K.M.S. Invs., 331 N.W.2d 907, 913-15 (Minn. 1983) (where resident manager with criminal history entered tenant's apartment using a master key and raped tenant, liability imposed based on negligent hiring); Vermes v. American Dist. Tel. Co., 312 Minn. 33, 41, 251 N.W.2d 101, 105 (1977) (liability imposed based on landlord's failure to make lessee aware of facts tending to make the premises insecure for lessee’s jewelry business).