Mont. Code Ann. § 41-3-1327

If a petitioner in a child custody proceeding under this part has improperly removed an Indian child from the custody of the parent or Indian custodian or has improperly retained custody after a visit or other temporary relinquishment of custody, the court shall decline jurisdiction over the petition and shall immediately return the Indian child to the parent or Indian custodian unless returning the Indian child to the parent or Indian custodian would subject the Indian child to substantial and immediate danger or threat of substantial or immediate danger.