Dom and Kay start new roles at MI5, but each of them struggles to find their place. Dom takes a big gamble to impress a senior agent, sparking a dangerous chain of events.

Dom races to fix the situation before she’s exposed, but Kay urges honesty. Things worsen when Dom is threatened by someone from her past, while Kay doubts if the MI5's way of life is for him.

Dom ropes in Kay to help her gather evidence about Steve, and the pair trace him to a mysterious lock-up. Tevin piles on the pressure, and Kay gives Dom an ultimatum.

Dom and Kay try to ambush Steve by breaking into his flat, but plans go awry. Kay’s loyalty is pushed to breaking point.

After being dismissed from MI5, Dom and Kay go their separate ways – but will new clues about a possible threat to the Notting Hill Carnival pull them back together?

Dom and Kay race to stop a looming threat at the Notting Hill Carnival, while a shocking twist reveals an unexpected enemy.