The adventures of the choristers 5 - The Head

Again the Choir Kids find themselves in a mystery to resolve.
After the frightening end in the adventure of "The monster of the labyrinth", the same head appears in this adventure, where the choristers on transfer for a concert are risking their lives when a choristers goes missing between magic and mystery.
Will our small choir kids save the missing chorister?
How will they resolve also this mystery before it's too late?