The relationship between Scott (Tyler Posey) and Allison (Crystal Reed) has turned to the bottom, but they still have to guard against Allison's father Argent (JR Bourne). Jackson (Colton Haynes) hopes to become a werewolf after being bitten by Derek (Tyler Hoechlin), but black liquid always flows out of his nose. Derek reminds him that this is the body's rejection. And his girlfriend Lydia (Holland Roden) seems to have lost a memory after being bitten by Derek's uncle, and she has become strange. There have been a series of murders in the town, and the perpetrators are not werewolves, but another unknown species that releases toxins when killing people. Scott, Derek and Argent are all looking for this creature, and it is always one step ahead of them. What exactly is this species? Will Jackson's transformation be successful? What secrets are hidden behind Lydia's amnesia?