WARNING: The following contains spoilers for The Third Day Episode 6, "Last Day -- The Dark," now airing on HBO.
HBO's The Third Day makes it hard to envision Sam (Jude Law) as someone who could really undo the tyranny sweeping over Osea Island. However, he's never given the impression he could fight, and he's always seemed scared when the natives warned of "the dark" coming to engulf him.
Well, the Season 1 finale reveals what this darkness is, and it has to do with the mad blood running through Sam's veins as he tries to protect Helen and their daughters, Lu and Ellie.
Sam doesn't rise up when Jess starts a coup on the island so their daughter, Epona, can depose Sam and become the "Mother." He's annoyingly passive, deluded that his dead son Nathan is still alive and not grasping Helen and the girls could be murdered. Even as Jess' crew takes them hostage and murders Mrs. Martin, Helen needs Sam to become an alpha, but he doesn't have it in him -- at least until Lu rescues them from captivity and Helen makes it clear that if he doesn't unleash the rage, they'll die.
Clues have been dropped Sam wanted to kill people when Nathan was abducted years ago, and now, Helen wants him to channel this anger. Luckily, when he sees Lu terrified and remembers Ellie's still under Jess' watch, Sam goes into killer-mode. His eyes dilate and he becomes someone else, going downstairs and brutally stabbing up, Jason, the man watching Ellie. He had a relationship with Jason, so one might have assumed Sam would show remorse, but he plunges the knife in and out multiple times in a gory scene. Ellie's scared because her dad has a crazed look on his face from all the blood, made even worse by him enjoying the slaughter.
Sam has finally accepted his new persona, which is tied back to his bloodline as the Charringtons descended from Jack the Ripper. Jack killed on the streets of England as part of some belief he was purifying the Earth, and now, Sam's executing a similar bloodbath, but for a different purpose. He knew he had this in him, but he was suppressing it all the time, as the iconography of Jack killing people was littered all over the island. However, with this newfound anger, Sam grabs a gun and goes to the nearby church to embrace his new side.
He encounters Tomo and Larry with a mysterious kid pretending to be Nathan, and in front of all the girls, he kills them with a shotgun. Ironically, it's near the Celtic pagan altar, which Sam soaks in as a sacrifice to set things right. Understandably, his family is afraid, as they've never seen him move or act this way. But, as he snaps out of this berserker mode, the ladies are grateful he became this monster. However, he knows he can't go back home because "the dark" has changed him, tethering him to Osea until he dies. It's for that reason he gives them the money he stole from Helen and urges them to escape, opting to stay behind as penance.
HBO's The Third Day stars Jude Law, Naomie Harris, Katherine Waterston, Nico Parker, Charlotte Gairdner-Mihell, Paddy Considine and Emily Watson.