The Ring of ThothEdit
This is a very old item from way back when the ancient Egyptions roamed the Earth. It was sent to Cass in a treasure chest by The Jester, which she wore on her finger for the rest of the school year.
When they take a field trip to the Egyption Museum, Cass sees Thoth's mummy and touches his finger. It breaks and flies into Yo-Yoji's hand. Luckily Cass is not in too much trouble for this.
Pietro tells them that placing the ring on the mummy's finger could reveal a lot of what Cass needs to know to finding out the secet. So the trio heads out into the museum to place it on his finger. When they get there the mummy is gone! And everyone suspects that they stole it.
Not only that, but they're racing to get to placing the ring on the mummy before the Midnight Sun does.
In the end, SPOILER ALERT!!!!!!!!!!!!!!! V
Cass does put the ring on his finger and it takes her through some sort of mental walk through where she does find out the secret to the Other Side.