Plot summary
Felix, Sarah and Mrs. S arrive in London to meet with Terrance who believes Ethan's coded numbers relate to a prisoner identity. As Terrance investigates, Ferdinand has him beaten to death. Cosima comes to believe that Shay is a spy working for Castor. When Delphine interrogates Shay, she intends to stage her death as a suicide. However, Cosima calls her off because Gracie admits that she betrayed them to help Mark. Pouchie demands that Donnie return the drugs, keeping the canister with Helena's eggs as collateral. Donnie and Helena return the drugs, but Helena kills Pouchie and his crew after they threaten Alison's children, and takes all of the money.
Mrs. S previously stated that to stop all the danger, the only way is to kill the original source; but when the dying Terrance whispers what he found out, Mrs. S insists that she, Sarah and Felix return home and stop investigating. Sarah takes Terrance's phone, leading to the address of Kendall Mallone, Siobhan's mother. Kendall reveals that she submitted to Ethan's medical tests while in prison, and she is the original to both Leda and Castor as she is a chimera carrying two genetic lines; Kendall absorbed a male twin in her mother's womb.
Credits
Adapted from Wikipedia contributors, List of Orphan Black episodes. HTML formatting and reference markers removed.