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 confronted by Osman about sensitive issues; 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.