When the British Government receives a threat signifying Scorpia's return, Blunt and the Department begin the hunt. Meanwhile, in Malta, Alex follows the scientist working for them to his secret lab aboard a decommissioned ship.

Alex has been captured and Tom, Kyra, and Jack must scramble to find him. As Scorpia shows 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.

Alex is sent on a mission for Scorpia to prove his loyalty, with Tom and Kyra following close behind hoping to rescue him. Meanwhile, the Department attempts 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 orchestrates the final stages of their plan to threaten the lives of an entire city, Alex must go back undercover in a desperate bid to stop Julia Rothman before it's too late.