It has all the makings of a gripping spy novel.
Two young men accused of passing secrets to China, who vigorously protest their innocence, are swept up in a swirling political intrigue with a shadowy semi-mythical figure (in the shape of veteran Downing Street national security adviser Jonathan Powell) at its heart. Yet the story dominating domestic headlines as MPs returned from recess this week is not fiction, or at least not entirely.
