Grotto plot
Three kids force a classmate to take a test of bravery to be accepted into their group. He must find a skull in an abandoned church. There he falls through a crack in the church floor. The other three come to the rescue and call out to him in vain. The sister of one of them has followed them and they lower her into the hole to see where the classmate has gone. Unfortunately, all four of them also fall through the crack. Down below they will have to make their way out of the caves there, aided by the stalagmite creature Grotto they encounter there.