Ep 6. Persephone

In MI-5 season 3 episode 6 titled Persephone, tension is high with the threat of a terrorist attack looming over London. The team is preoccupied with stopping a cell of extremists known as the Phoenix group, who are planning a devastating assault on the city. MI-5's top analyst, Sam Buxton, gets a lead on a possible connection between the Phoenix group and a former American soldier named Neil Baxter.

In the meantime, Adam Carter, a newly reinstated MI-5 officer, faces his own personal demons. Adam's wife Fiona had been killed in a terrorist attack two years ago, and he finds himself drawn to her sister, Laura. Laura is still struggling to cope with the loss of her sister and doesn't want anything to do with Adam. But as the episode progresses, they find themselves forced to work together to thwart the Phoenix group's plans.

Meanwhile, Tom Quinn, the team leader, is still reeling from the revelation that his girlfriend, Ellie, is actually a spy. He's struggling to reconcile his feelings for her with the fact that she's been lying to him all along. Tom confronts Ellie about her betrayal, and surprisingly, she reveals that she's been spying on MI-5 for a rival intelligence agency to protect her father, who had been imprisoned for spying in the past.

As the Phoenix group's plans become clearer, MI-5 realizes that they're planning to use a chemical weapon in their attack. The team shifts their focus towards locating the weapon and finding out where the group is planning to deploy it. They finally hone in on a suspect, but when the suspect is taken into custody, he claims that someone else is planning the attack. The clock is ticking, and MI-5 has to race against time to uncover the truth and prevent the attack before it's too late.

Persephone is a tense and gripping episode, with a lot of emotional twists and turns. The personal relationships and struggles of the MI-5 team members are woven seamlessly into the overarching plot of the Phoenix group's threat, adding depth and complexity to the story. As always, the show's attention to detail and realistic portrayal of the intelligence world make it a must-watch for fans of the spy genre.