Rei/Sailor Mars and her mysterious ally are both on a dangerous quest together to find a part of the lost past that could hold a key to the future. But the forces of evil are in hot pursuit and now it's up to their friends the Mystery Shack Investigators, Sailor Senchi, and M.A.S.K. to find them before they do.
The evil Gideon continues his hunt for the lost Grimores, one is hidden in a old military base in Gravity Falls. Ami Mitzuno and someone from her past Ryo Urawa are both forced into the hunt. But both are venturing into unholy ground for unfortunately both aren't alone, for evil from the past doesn't rest.