As the Department receive a horrifying threat against the United Kingdom, Alex follows the trail of a shady scientist working for Scorpia to a secret laboratory aboard a decommissioned ship.

Alex has been captured and Tom, Kyra and Jack must scramble to find him. As Scorpia demonstrate the power of their new weapon, Invisible Sword, Alex is confronted by Julia Rothman with some uncomfortable truths about his father.

Cut off from his friends and forced to work with one of his greatest foes, Alex endures a punishing induction to Scorpia, and must face off against a gang of ruthless trainee assassins.

To prove his loyalty Alex is sent on a mission for Scorpia, with Tom and Kyra following close behind hoping to rescue him. Meanwhile the Department attempt to unlock the secret of Invisible Sword.

Alex returns home with a dark mission of revenge. Jack, Tom and Kyra must enlist the help of unlikely allies to save Alex before he commits to Scorpia forever.

Captured and questioned by the Department, Alex must rely on his friends to remind him who he truly is. But are there still truths about his past the Department haven't told him?

As Scorpia orchestrate the final stages of their plan to threaten the lives of an entire British city, Alex must again go back undercover in a desperate bid to stop Julia Rothman before it's too late.