Lab Rats (2012)

S4E15 One of Us

Adam, Bree, and Chase are on a mission to find Leo, who has not shown up for training. They soon discover that he’s in Mission Creek, dealing with the fallout from Janelle's ultimatum about their relationship. Suddenly, S-1 makes an unexpected appearance, leaving everyone stunned. She’s arrived on the island with no memories, just like the rest, but is haunted by recurring flashbacks of Krane.