The Secret Series is a series of 'secret'-themed fantasy adventure novels written by Pseudonymous Bosch (Raphael Simon).

The series centers on three middle school children: Cass, Max-Ernest, and Yo-Yoji; and their adventures as members of the Terces Society, a group that seeks to prevent a mysterious "Secret" from being discovered by the villainous organization of alchemists, the Midnight Sun.

The Secret Series is inspired by Lemony Snicket's A Series of Unfortunate Events and targeted at middle-school-aged readers.

[1] As of 2021[update], a film adaptation is in development.

[3] Additionally, the plot of each book contains an item or object that relates to the sense the book surrounds.