Rapunzel and the Lost Lagoon: A Tangled NovelLeila Howland2017

Rapunzel is not your typical princess. For one thing, she has returned to her kingdom after eighteen years spent trapped in a tower and she's still getting to know her parents. For another, she has to get used to royal customs, like the proper ways to sit and curtsy, when she'd really rather climb a tree and paint. Plus, she hates wearing shoes.
Cassandra is not your typical lady-in-waiting. As the daughter of the captain of the guard, she has grown up fascinated by security and weaponry. It has been her life's goal to become a soldier in the guard, and princess-sitting doesn't really fit into her plan-especially when that princess's aggravating boyfriend is always hanging around.

But when Rapunzel and Cassandra stumble upon a secret lagoon said to hold the key to the kingdom's greatest power, it will be up to them to solve the mystery before someone more sinister does.