I think its really interesting how Cass goes back in time to find a very important unknown secret. This secret could be anything! She doesn't even have an idea of its subject but yet her mind takes her back over 500 years to go on this adventure. Now her reason to this is the Terces Society needs this secret to go on with all of their missions.  But what I think is that she wants to learn about herself and her past. She recently found out she was adopted this filled a void she had for on long time, but not completely. She still didn't know who her biological parents were. I think that Cass felt if she figured out this secret then her life would be complete and she would know everything needed to know.

Not true. When she went back in time she spoke to the Jester (her great great great great... grandfather) and asked him for the secret. He told her he had no such thing as a secret yet and he would tell once he had one. They found a place were 500 years from now the secret would be kept safely. Under a special lodestone. After Cass had heard this she thought, I know where the secret will be now so my mission of the past is complete. Yet she stayed in the past world. I think she wanted to figure out more of her family. Just what would happen that would lead her to life.

Later on she finds the loadstone inside of it is a clue. It says
As Above So Below
She is confused. Later on she receives a package thats say her name on it dating from many many years ago (it was even on the mayflower) In it is a big treasure chest once it is opened she finds a million gold coins, jewels, golden goblets. But she is very dissapointed, this hasnt givin her any information on her past just riches. I think that the chest was a prize and that the clue inside the loadstone was the secret. As Above So Below means to me what happened once is connected to what is happening now so if you want to find the secret you don't need to go 500 years back, but you need to find what is most important and learn that if you look too closey at the past and what you wish for and can't have then you will not acomplish anything you have to move forward in life.