He had his pack kidnap Clary Fray in hopes to getting the Mortal Cup. At Jade Wolf, he threatened the life of her mundane friend Simon Lewis, after which Clary lied to him about the Cup being at their loft to buy them some time. When Simon started a fire in the locker room that caused the alarms and sprinklers to go off, Theo instructed his men to find the source while he threw Clary into a shipping container and locked her in.
When Shadowhunters arrived to rescue Clary, Theo and the other werewolves prepared to stop them. However, Luke, in an attempt to save Clary, attacked him, thus challenging his alpha position. He was killed in the tussle, and Luke replaced him as the pack's alpha.
- 1x05: Moo Shu to Go (first and only appearance)