Travelling to Malta in search of answers about his father's past, Alex and his best friends Tom and Kyra uncover the beginnings of a deadly plot by the criminal cabal known as Scorpia, and the identity of its charismatic and ambitious new leader.

When the British Government receives a horrifying terrorist threat signifying Scorpia's return, Alan Blunt and the Department begin to hunt for their old enemy. Meanwhile in Malta, Alex follows the trail of the shady scientist working for them to his secret laboratory aboard a decommissioned ship.

Alex has been captured and Tom, Kyra and Jack must scramble to find him. As Scorpia demonstrates 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 British city, Alex must go back undercover in a desperate bid to stop Julia Rothman before it's too late.