The Seductive Scent of Empire. Tales of MI7, #15

When Ruby Parker, Head of MI7's Red Department, is hospitalised by a burglar, all is not as it seems. Her removal coincides with a series of catastrophes for British spies in hostile territories abroad, and some very shifty behaviour by the new Acting Head of Red Department, Patrick Atherton. Atherton dislikes Red's established hierarchy, which includes all its officers without exception, and possibly John Mordred in particular.
The idea that there's something fishy going on, and that all this is linked, seems intuitively obvious, and probably worth investigating. But then things take a turn for the strange. Atherton has an apparent breakdown; he gets up from his desk, leaves Thames House and apparently goes off radar. Important men and women across London start dying in violent circumstances. It simultaneously transpires that the mysterious Black Department is taking a close interest in all this.
And not quite from its usual distance. Suddenly, John Mordred himself becomes the focus of intensely hostile scrutiny. And when he, too, goes off radar, it's because he no longer has a choice. At least, not if he wants to live. For a while, nothing seems to make sense. Then, shockingly, it does.