The Killing (CHERUB #4) by Robert Muchamore

Leon is a small time crook who's ridden his luck for three decades. When he starts splashing big money around, the cops are desperate to know where it came from.

James' latest mission looks routine: make friends with Leon's kids, infiltrate his home and dig up some leads.

But the plot James begins to unravel isn't what anyone expected. And the only person who might know the truth is an eighteen-year-old boy.

There's just one problem. The boy fell to his death thirteen months earlier.