Slim Parsons is all but burned. When her last deep-cover job for MI5 ended with a life-and-death struggle on a
private jet, she went on the run from her deadly target - a conniving businessman and money launderer codenamed "Hagfish." Now she's back at home, in hiding from her angry bosses in the Security Service, who have accused her of being overly violent and unsuitable for the role of an MI5 operative.

But after several months off the grid, Slim is called back to another job - Operation Linesman - where she is
asked to infiltrate a news website Middle Kingdom whose explosive articles clearly show that they've hacked into the most high-security government databases. She accepts the assignment on condition that the Security Service
searches for her missing brother.

But Linesman turns out to be anything but simple. Slim uncovers a curious connection between the Middle Kingdom hackers and the legendary Bletchley Park codebreakers. Her new colleagues are becoming suspicious of her intentions, and Hagfish is out for revenge and threatening MI5 itself as it all comes together in a shocking crescendo.

And all the while she is being watched by someone even deeper in the shadows than she is.