The Skeleton Key

Seichan wakes in a Paris hotel with a deadly collar around her neck and only a limited time to survive. Forced into a dangerous bargain, she must help rescue a captive young man and track down the son of a powerful enemy.

The chase drives her into the catacombs beneath Paris, where she and an uneasy ally navigate an underground maze of bones, secrets, and threats. The mission pulls her between rival enemies while the clock keeps ticking toward catastrophe.

As the pressure mounts, the story becomes a survival race built around coercion, betrayal, and a looming bombing threat. It also serves as a brief lead-in to the next Sigma Force installment, with the action ending in a way that points forward rather than fully concluding the larger arc.