Covert CIA agent Martian is called back to London Station. An incident in Belarus puts Bosko and Henry on a collision course with Langley. Danny learns a lesson, and someone unexpectedly reappears in Martian's life.

Dr. Blake arrives from Langley and is put to a test by Martian and Henry. A spooked source threatens to put an operation at risk. Danny's cover is put in play. Martian, overtaken by events, begins to question Sami's motives.

Henry questions Martian's thinking. Bosko is briefed by Langley on a top-secret operation. Poppy makes a startling discovery. Martian confronts Sami about why she's in London and finds a needle in a haystack, before a heated session with Dr. Blake.

Henry and Martian wade into a diplomatic incident with the Belarusian delegation; dropped into her mission by Naomi, Danny walks a tightrope. Poppy and Martian attempt a fresh start. Osman threatens Sami.

Feeling the heat from Langley, Henry sends Owen to hunt for clues in Minsk; Danny's work with Reza generates an unexpected outcome; Sami is approached by Mr. Dalaga about a sensitive issue; Martian, seeing the size of the stakes, sets a rat trap.

Richardson's arrival at the Fishbowl catches Henry off guard; Martian scrambles to unravel Cossack's game as the stakes escalate; Naomi, uncovering a secret, cautions Danny; Sami's attempts to reach Martian lead to naught and Osman plays his hand.

Mr. Dalaga ups the pressure on Sami. Bosko is briefed on the scope of Valhalla. Jerome is advised to listen to his horoscope. Martian's hand is forced when Poppy's life is under threat; with Henry and the team he strategizes a high-risk recruitment.

Martian's recruitment doesn't go to plan. Richardson breaks down the Chinese play for Bosko. Blair uncovers an inroad to Volchok as Henry reminds Dr. Blake what's at stake. Danny wrestles with her conscience. Sami makes a startling confession.

Martian buys time with a crystal ball bluff to Langley; Blair and Owen hunt out a White Rabbit; Osman raises the stakes; Henry tasks Dr. Blake with an urgent assessment; Danny crosses the Rubicon; with a green light from Bosko, a trap is sprung.

As command of the operation shifts out his hands, Bosko shares a grim reality; Naomi receives troubling news out of Iran; Richardson runs a rogue operation; Felix gets overtaken by events; Martian, desperate, makes a devil's bargain.