A brutal assault thrusts newly appointed head of SO15, Rachel Carey, into the center of a conspiracy far more perilous than any she has previously faced.

Fresh footage documenting the assault surfaces, deepening Carey’s sense of isolation from everyone near her. As the urgency to identify the attacker intensifies, Carey seeks support from unexpected sources.

Carey pursues a single suspect, while Napier handles another. With each piece of evidence that emerges, Carey finds herself racing to prevent a looming disaster—has she miscalculated gravely?

The demands on Carey to bring Whitlock to account are intensifying, yet her focus is drawn elsewhere; with Napier effectively vanished, more pressing concerns loom. A palpable loss of faith amongst Pierson's team escalates into something pe…

Bound together by circumstance, Carey and Pierson fled deeper into a labyrinth of hidden tunnels. As they ran, shadows from Pierson's history began to close in, and at last, the secrets surrounding Simon were brought to light.

Carey has reclaimed leadership of SO15, yet a daring maneuver by Figgis presents her with a devastating dilemma: what lengths will she traverse to safeguard the truth?