The Last Chimera is definitely a beast. It's big, and it seemed to have come out of nowhere, but don't worry, Sciles is on the case! Stiles turns to Scott with what his investigation found - there's another way into the building that the Last Chimera came out of. While Stiles and Scott are investigating, they run into Tracey.
Theo bonds with all of his pack. He does normal things like taking Tracey to go kill a guy, and Theo gets Josh high by electrocuting him. Theo and his pack are just totally normal people with regular hobbies. Then, he tells Hayden to basically listen to everything he says and that she can't keep secrets from him. He's such a charmer. Theo likes to remind his pack that he's in control.
Thankfully, there are also good influences in this world. Sheriff has a heart to heart with Stiles to encourage Stiles to forgive himself for killing Donovan in self defense. The Sheriff also recommends that Stiles try to forgive Scott. Then, there's Mason being a bestie to Liam. Mason helps Liam try to get some information on Theo and his chimera pack, and Mason also convinces Liam to talk to Scott.
The writings on the floor actually reveal that the Last Chimera, the Beast, is actually something old. The Dread Doctors resurrected a creature, and according to Gerard, the Beast has a tie to the Argent family.