DI Helen Birch is recovering from major surgery, housebound and exceptionally bored. Her boss, DCI McLeod, has made it crystal clear: she is not to take on any work until her recuperation is over.
In her absence, Amy Kato is promoted to sergeant and is given a maddening case to work on: Edinburgh is being plagued by an anonymous vigilante. He started small, meting out punishment to obnoxious boy racers and other antisocial folk, but his behaviour is escalating.
Amy can tell from the anonymous online paper trail he leaves. His writings are increasingly confident, and increasingly threatening. And yet he also seems to be invisible: her team can find no clue as to his identity, and no trace of his whereabouts.
At first, McLeod doesn't see the case as a huge deal.
Concerned, Amy comes to Birch in secret to ask for help, and Birch finds it impossible to resist taking action: placing her directly in the path of immense danger ...
