WARNING: The following contains spoilers for The Third Day Episode 5, "Tuesday -- The Daughter," now airing on HBO.
Since Sam came to Osea Island, HBO's The Third Day has laid down eerie clues regarding the influence Jack the Ripper has had on the place. Sam was taken aback to see the Martins' inn hosting so many pictures of Jack killing women, which the islanders said was simply a plot to capitalize on tourists' fascinations. However, as the "Winter" arc rolls on, fans discover Jack has a dark connection to Osea's origin, and it's why Sam has been having psychotic breakdowns.
When Sam and Helen's daughter, Ellie, connects with Jess' daughter, Kail, it's over religion and how being God's children can save them. Kail ends up whisking Ellie away to a bunker, which serves as a Celtic sacrificial chamber. There's a shrine dedicated towards the island's warped version of paganism and Christianity, as well as more images of Jack killing women. Here, viewers learn Jack's actually the founder of the island, Frederick Charrington, aka Sam's ancestor.
Ellie doesn't know Sam's alive or that he's a Charrington, so she's intrigued as Kail talks about how Jack killed other to bring balance to the world. It's said that Osea is Earth's heartbeat, and to ensure Osea kept beating, Frederick attacked and killed women as a way of appeasing the gods.
Ellie hints this is the ultimate sacrifice to God, removing those who would tarnish the images of the saints. When Frederick, whose family dealt in the brewery business, came to Osea, he apparently wanted everyone to be free and absolved of their sins. It's why he continued to push for sacrifices, with his mad blood passed down from generation to generation. Theorists believe this is why Sam has had dreams about death, gore and mutilation, especially with scenes hinting it's women and young girls being killed. They think this is Jack's murder gene being passed on, leaving them wondering if the eccentric Ellie has the same problem as her dad.
She's become awfully reclusive, turning to religion over her family, which Helen doesn't like. Kail is preying on this and working her the same way Frederick manipulated the first Osea islanders. She wants her to buy into the past, where the trends of murder and sacrifice were passed on and normalized, explaining why the inhabitants love Jack, as he was their first "Father."
Given how crazy and ragged Sam looks when Helen (aka Cas) finally finds him, it appears Jack may have crept into his mind, which could fulfil a prophecy. In the "Summer" arc, audiences saw an ominous image of Sam trying to murder people, and now they know it's because the new king has the blood of a serial killer in him, which spells trouble for his wife and daughters.
Starring Jude Law, Naomie Harris, Katherine Waterston, Nico Parker, Charlotte Gairdner-Mihell, Paddy Considine and Emily Watson, The Third Day airs Mondays at 9 p.m. ET/PT on HBO.