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.