The treasures were scared of Plumwood and were hidden by the Winkler's and Beckett's during construction of Plumwood. When the treasures are put together, the stone works to bring back the dead. The treasures are wanted by Mr. Winkler and his Bloody Knights so that they can be the most powerful witches and wizards in the wizarding world. Boo wants to get the treasures before Mr. Winkler for McGonagall to hide again in a different place.
In The Wand , Mr. Winkler sneaks into McGonagall's office and gets the first treasure which was the wand. At the end of this episode, McGonagall gives Boo the key to the second treasure but Mr. Winkler gets the key and gets the cloak in The Cloak.
In the Book you learn who hid the treasures and more about why Mr. Winkler killed Sink Ghost.
In the Picture Frame, Roseia revealed that her stone necklaces is one of the replicas of one of the treasures.
In the Cellar, Boo and Roseia are forced to try to get the next treasure the Ball of Light for Mr. Winkler. But they do not it is revealed. It is also revealed that they escaped him.
In the Ball of Light, Mr. Winkler gets his hands on the Ball of Light.
In the Battle Part 2, Boo and Caretaker find the last treasure which is the Stone.
In the Battle Part 3, Boo and his friends put the treasures together to bring back the Caretaker.