Concurring Opinion.
Achor, C. J.— A question is presented as to whether appeal rather than the proceedings in mandate is re*543lators’ proper remedy. This issue is not discussed in the majority opinion.
The jurisdiction of this court to issue writs of mandate is governed by statute. Burns’ Ind. Stat. Anno. §3-2201 (1964 Cum. Supp.). It is an extraordinary remedy not to be used as a substitute for an appeal but only to be applied where the lower court fails to perform a duty enjoined on it by law. State ex rel. Hashfield v. Warrick Cir. Ct. (1961), 242 Ind. 318, 178 N. E. 2d 734; State ex rel. Rans v. Fulton Cir. Ct. (1960), 240 Ind. 288, 164 N. E. 2d 111; State ex rel. Botkin v. Delaware Cir. Ct. (1960), 240 Ind. 261, 162 N. E. 2d 611. It will not lie to control the exercise of discretion by the trial court. State ex rel. Beatty v. Nichols (1954), 233 Ind. 432, 120 N. E. 2d 407; State ex rel. Steers v. Hancock Cir. Ct. (1953), 232 Ind. 384, 112 N. E. 2d 855.
On the other hand, mandate will issue to compel a court to act where there is a clear legal duty to act. Burns’ Ind. Stat. Anno. §3-2201, supra; see also: State ex rel. Steers v. Hancock Circuit Ct., supra.
In this case the relators are currently exercising the custodial care of the child whose custody was placed in issue. They had exercised that custodial care over several years with the consent or acquiescence of the divorced parents of the child. There was an open controversy as to the continued custody of the child which threatened its welfare. Any order with regard to the custody of the child while it was in the custodial care of the relators could not be conclusive as to relators’ rights unless relators were made a party to the proceedings. Henderson v. Kleinman (1953), 231 Ind. 657, 109 N. E. 2d 905; Bryan v. Lyon (1885), 104 Ind. 227, 3 N. E. 880. Therefore, in the present case, relators were necessary parties in any proceedings to modify the *544original order of custody and as necessary parties their right to intervene was absolute. See: Noblitt v. Metropolitan Plan Commission (1961), 131 Ind. App. 497, 172 N. E. 2d 580.
The statute provides: “When a complete determination' of the controversy cannot be had without the presence- of other parties, the court must cause them to be joined as proper parties.” Burns’ Ind. Stat. Anno. §2-222 (1946 Replacement) (Emphasis added).
Since, under the facts presented the relators are necessary parties, the court had no discretion in allowing them to intervene; rather their right to do so was absolute.
Furthermore, because of the long delay with normally occurs in the appellate process, an appeal on the issue presented would not have constituted an adequate remedy at law. The mental health of the child involved could only suffer as a result of such protracted litigation.
For the above reasons it is my opinion that the writ of mandate was a proper remedy.