Gray Salvation — Alan McDermott

When the body of an MI5 operative is found floating in the Thames, police frogmen find a significant clue nearby: Nikolai Sereyev, an MI5 informer and mid-level player in a Russian criminal organization. Both men have been brutally murdered.

Andrew Harvey is tasked with finding his colleague's killer, and quickly uncovers a plot to assassinate a visiting dignitary on British soil. No sooner has he scraped the surface of the case than the tables are turned and he becomes a pawn in a game of international brinkmanship that leads all the way to the Kremlin.

Harvey's girlfriend, Sarah, also a secret service operative, is hot on his trail, but when she too becomes compromised, security chief Veronica Ellis knows there is only one man she can turn to. He's a loose cannon, but she needs his help to rescue her agent and prevent a full-blown international incident.

The trouble is, Tom Gray has gone to ground. Finding him is just the beginning.

This book is the sixth in the series but can be enjoyed equally as a standalone novel.