Daniel Sharman as Isaac Lahey -Werewolf-
Isaac Lahey is a Beta werewolf, Allison’s second boyfriend, and Scott’s close friend and former roommate. Isaac was Bitten by Derek Hale as an Alpha werewolf. In the past Isaac was abused and tormented by his father, who tortured him by often locking him in their basement freezer. His mother is also deceased and his older brother Camden was killed in combat overseas. Isaac was the first member of Derek’s Pack, though he joins Scott’s Pack later on. Isaac asked to become a werewolf to feel powerful and confident after all the abuse from his father, who is murdered by the Kanima at the beginning of Season 2.
Isaac was the first of Derek’s Beta werewolves to gain control of his animal side during the full moon, and in spite of his dark family-life, Isaac has good intentions and a warm heart. At first, Isaac did not like Scott and did not trust him, because he believed Scott was a loser because he wondered how Scott survived so long without a pack. Nevertheless, he eventually trusted Scott when he realized he has good intentions, and becomes friends with him. Among the dangerous events throughout Season 2, Isaac sides with Scott, revealing that he trusts him and holds onto Scott’s friendship because he doesn’t have anyone there for him. He helps Scott against Gerard when Gerard takes control of the Kanima, but he is stabbed by Allison. After Jackson is cured of being a Kanima and Gerard’s defeat, Isaac stays as a part of Derek’s Pack instead of following Boyd and Erica, but holds onto Scott’s friendship.
At the start of Season 3A, Isaac is revealed to have found where the Alphas have been keeping Erica and Boyd, however he was attacked by them and had his memory wiped. Isaac was rescued by a mysterious woman. To cure his amnesia, Dr. Deaton helps Isaac remember the night he had his memory wiped using an ice bath and remembers that Erica is already dead, while Boyd is being held captive by the Alphas with another werewolf named Cora. He later participates in helping Scott and Derek capture Boyd and Cora, who are rabid from the full moon with assistance from Chris Argent. Isaac takes on a despise the twins, Aiden and Ethan, blaming them for the supposed death of the girl who saved him and the numerous sacrifices, and stands off against them. Allison apologizes to Isaac for attacking him back in Season 2 and assists him in his vendetta against the twins. He teams up with her against the threats throughout the season becoming closer, eventually forgiving and developing feelings for her. After being thrown out of Derek’s loft by Derek to protect him from Derek himself, he moves in with Scott and Melissa. In “Alpha Pact”, Isaac later becomes fed up over Derek’s intentions, the deaths of Boyd and Erica, and confronts him about how people always get hurt around him and his pursuit of power, leading to him rejecting Derek as his Alpha and leaving Derek’s Pack. Isaac is chosen to be Allison’s tether when she undertakes a dangerous druid ritual to find her father. During the mid-season finale, he helps Allison, Stiles, and Scott find their parents. With Scott becoming a True Alpha, Isaac joins his Pack.
In “Anchors”, Isaac starts acting on his feelings towards Allison, even attempting to kiss her, following her for her protection and arriving at her apartment, to her mutual consent. He is open about this with Scott who is evidently uncomfortable at their budding relationship. Isaac still holds a grudge towards Ethan and Aiden saying they can’t join Scott’s Pack because of their part in Boyd’s murder and taking glee when Scott says no. After helping Allison with research on William Barrow, Isaac is confronted and “tagged” by the Oni. He later helps Allison and Chris retrieve information about the Oni, Kitsune and the Nogitsune from the Yakuza recluse, Katashi “Silver finger”. He and Allison affirm their feelings for each other when Allison kisses him. Isaac is induced into a coma in “Letharia Vulpina”, saving Allison from stepping into electrified water as one of the traps set by the Nogitsune possessing Stiles. In “De-Void”, Isaac comes out of his coma and heals from his injuries, to Allison’s happiness and they spend the night together, consummating their relationship. In “Insatiable”, after Isaac is freed from the Nogitsune’s possession, Isaac assists in looking for Lydia. He and Allison share a moment where he assures her he was himself during their night together before the Nogitsune infected him. After arriving at Oak Creek, Isaac fights alongside Allison and Kira against the now Nogitsune-controlled Oni. He is eventually outmatched and by the Oni. He is saved by Allison, who is fatally stabbed by the Oni right afterward. Visibly shocked and stricken, Isaac watches on as Allison dies in Scott’s arms. In “The Divine Move”, Isaac is devastated by Allison’s death and finds comfort from Chris. Later, Isaac figures out that she had discovered that silver was the Oni’s weakness and that her arrows could destroy them. Chris and Isaac head to the school with the arrowheads and kill the remaining Oni. After Scott and Kira exorcise the Nogitsune, Isaac seals the dark spirit in Derek’s triskele box. At the end of Season 3B, Isaac decides to leave Beacon Hills, moving out of Scott’s house and heading off with Chris to France to put away the Nogitsune for good, and help Chris cope with Allison’s death.