Dr. Helen Magnus fights to save the life of one of the Sanctuary's research scientists who was viciously attacked by a seemingly docile Abnormal. Baffled by the creature's uncharacteristic behavior, Henry tries to figure out what, or who, caused the domesticated Abnormal to react so violently.

Magnus and Will are called to make a straightforward retrieval of a rare Abnormal off the coast of Louisiana. With a commissioned helicopter, the retrieval is successful and their cargo securely on board. But as the pair starts heading back to the mainland, something causes the unusual sea creature to break loose.