DNA

Robert Gibson's murder looks almost exactly like the crime scene from a case that drove Joe Donovan into a breakdown and early retirement seven years earlier.

With Gibson's murder still unsolved, another body turns up murdered in nearly identical fashion-that of Philip White, a colleague and lover of Kate Donovan. Could the cuckolded scientist have killed White out of jealousy in a fugue state?

Now back as senior scientist in the Forensic Investigations Unit, Donovan doggedly pursues a serial killer who takes pretty blonde women as his victims. He thinks he knows not only the killer, but also the next target-Sharon Page.

When wealthy Stephen Parker is found shot through the chin in his swanky home, it seems like a robbery gone wrong. The evidence points to John Pinion, a self-proclaimed 'investment adviser' to whom Parker owed £8,000.

The entire FIU team rushes to a secluded air force base, where a cargo plane has landed with all of its passengers and crew stricken by an unknown illness. Authorities believe it's biological terrorism.