Unknown, alone, and fearing for your life: as PC Lucy Clayburn is about to find out, going undercover is the most dangerous work there is.
But, on the trail of a prolific female serial killer, there's no other option - and these murders are as brutal as they come. Lucy must step into the line of fire - a stranger in a criminal underworld that butchers anyone who crosses the line.
And, unknown to Lucy, she's already treading it...