This is British crime writing of the absolute highest calibre - superb, twisting plot, engaging characters who are nuanced and layered, smooth and stylish prose, and packing an emotional punch.

Two years after Charlie Matheson died in a car crash, a scarred woman using that name is sitting in a hospital bed drip-feeding her story to a disbelieving Detective Mark Nelson. She claims to have died and gone to hell for her sins, before returning from the dead. She’s crazy, right? Nelson knows people don’t come back from the dead. His first love Lise didn’t after she drowned on vacation, and neither did Detective David Grove’s three-year-old son, wrenched from his life, killed by a paedophile ring.

Both detectives have moved on (well, somewhat, kind of...), but as they each separately investigate mysterious incidents, a malevolent shadow starts coming to light. Could Charlie really be telling the truth? If so, what hell has she been through for two years? If not, just what game is being played?

As Nelson delves into Charlie's story, and pulls at the threads it reveals, there seem to be some eerie connections to the renowned case of the 50/50 Killer - but that was solved years ago. Just what is going on? In I KNOW WHO DID IT, Mosby's storytelling is like a dirty fingernail scratching your forearm in the dark. There's a constant, unsettling sense of menace, of lurking evil.

Mosby isn't afraid to wade deep into the darker end of the crime pool: child abduction, torture, good versus evil on a grand scale. But he tackles such issues authentically and in such a manner that it never feels schlock or 'torture porn'. Everything fits, and is necessary. His characters are complex and conflicted, drawing us in as readers as much as the plotline, which is intricately thatched.

Creepy and masterful, I KNOW WHO DID IT will spin your head, tug at your heart, and punch you in the gut. When you recover, you'll be scrabbling to grab another Steve Mosby tale.