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. Someone unexpectedly reappears in Martian's life. Series premiere.

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. Osman plays his hand.