Sister Agnes is taken from her valuable work with runaways at the hostel to catalogue books at the order's library, with mousy Catherine for company.
Or so it seems.
Sister Agnes finds she has a lot in common with mousy librarian Catherine.
She cannot believe that she is capable of murder and sets out to prove it.
Sister Agnes finds out more about the man Catherine claims to have murdered and resolves to look more deeply into this apparently open and shut case.
Sister Agnes's investigations take her to Derbyshire, where the murder was committed 11 years before.
Sister Agnes's investigations into the death of Dougie McVie lead to the solving of two murders and a child-snatching.