While a deadly hacker turns Britain upside down, Danny decides whether to reveal all to Will, MI5 hunts the source down to an Islamic mosque with the help of MI5's best computer programmers. But things get suspicious when Ruth, close onto the tail of the hacker, goes missing and so does a member of the special team...

The baby of a celebrity couple is kidnapped and they call in MI5. Fiona goes in undercover to gather more information about the couple against Adam's wishes.