The captive leech is identified and the squad uncovers a plan to exterminate mankind. Meanwhile, Michael searches for Kirsty, who seems to have been abducted.

The squad becomes interested in a shipment of mysterious crates from Brazil. Michael suspects Kirsty has been 'taken' and meets her to find out.

After a boy kills a priest, the squad discovers signs of infection among the schoolboys, even though none appear to have been bitten.

The squad investigate the attempted rape of a female barrister who it seems was apparently saved by a leech. They find that she has been attempting to have a child, and has been been impregnated in-vitro with her late husband's sperm, but the pregnancy is not normal.

Whilst investigating a suspicious hit-and-run by a car with blacked-out windows, the squad suspects that the son of a well-known businessman is a leech and decides to look into his financial activities.

Mike is dragged away from Jack's stag night by a terrified, yet unreliable, informant who's desperate to talk to Jack. Mike simply wants to stop him turning up at the reception, but when the informant turns up dead and Jack disappears, Mike finds himself being pulled into a dark underworld of which he knows nothing.