Plot summary
Ferdinand, having saved Sarah, convinces them to decrypt files that Rachel sent him, as the files could lead to Susan Duncan who can probably deal with Sarah's bot. After Leekie's head containing the bot is delivered to Cosima, she and Scott begin investigating its true purpose. Trina, mistaking Alison for Beth, confronts Alison in a diner for investigating Lifespring Fertility Clinic, having been a carrier and trusting Beth in confidence. Posing as a gay couple, Felix and Donnie visit the clinic looking for information on Brightborn conception technologies. With Alison becoming more emotional about her (in)fertility issues, Helena buries her expired nitrogen eggs and leaves the Hendrixes behind.
Sarah goes to M.K. for help decrypting Rachel's files. Realizing that Rachel and Sarah are collaborating with Ferdinand, M.K. lures him to Beth's house and tricks him into sitting on a pressure bomb. M.K. confronts him for the Helsinki event, which wiped out multiple clones and their friends and family, including M.K.'s best friend Niki, another Leda clone. The letters "M.K." were from clone number 3MK29A whose name was Veera Suominen, a clone that escaped the purge and now plans revenge on those responsible for the deaths.
Sarah turns up to stop M.K./Veera, needing Ferdinand alive to help remove the bot in her cheek, which Cosima has discovered is performing gene editing to change her DNA. M.K. leaves with Ferdinand's money. Mrs. S defuses the bomb and Sarah declares that her score with Ferdinand is even. Elsewhere, knowing Charlotte is sick, Rachel makes the case that Charlotte should be left to die, refusing to intervene with her illness as the data would be invaluable. Susan agrees but reveals that she knows of Rachel's contact with Ferdinand. Cosima and Scott watch the Brightborn Fertility information video, presented by Evie Cho.
Credits
Adapted from Wikipedia contributors, List of Orphan Black episodes. HTML formatting and reference markers removed.