When a Chinese snatch team arrive in London for a 48-hour visit, Section D's suspicion is aroused. This causes Beth Bailey to call on the services of Kai, a Chinese Security Services agent who she has been grooming to help infiltrate security.
Ruth Evershed goes undercover at QMK, a research facility, and discovers that the Chinese are looking for Jiang Lee, a scientist who has discovered a de-salinisation technique worth billions. Desperate to get hold of Lee, the Chinese will stop at nothing, but the UK cannot afford to lose an intellectual property of such value.
Meanwhile, a bomb is reported at QMK and Ruth quickly evacuates with Jiang Lee. However, it soon becomes clear that the bomb was merely a ruse to get Lee out in the open, and the team begin to believe that Kai might be a triple agent.
Later, there is suspicion from Section D on receiving a second bomb threat, but when they investigate they discover a bomb in central London. With minutes to spare they are under pressure to stop a catastrophic explosion and ensure Jiang Lee stays on British soil.
Amid the chaos, Lucas and Maya's relationship intensifies and he becomes increasingly distant from the team. Are Lucas's loyalties beginning to change as his past catches up with him?