That part of the back story gets sketched in efficiently. Tracy and childhood best friend Erin drink and do drugs, her academic career hasn’t worked out the way it was supposed to, and she feels overshadowed in her father's affections by her successful musician brother. At a club in Leeds, heavily under the weather, Tracy kisses Erin’s boyfriend Jaff, which predictably triggers the row that has Erin taking herself back home and taking something of Jaff's with her.
The something is, of course, the weapon, and the police search the shared house in Leeds looking for further evidence about the circumstances surrounding a case where the daughter's not saying anything to explain things.
There's the possibility that one of them may have twigged to the presence of Banks' daughter in the house, but she's not there when the raid happens, she's calling herself another name and she's got a touch of the hots for the house-mate's boyfriend.
Returning home after work to discover that the place has been raided and the third occupant, who was home at the time, has flushed away the dope stash as soon as the cops were off the scene, I guess Tracy/Francesca was always going to head over and warn Jaff, triggering a manhunt that's complicated by her decision to use her father's isolated house as a temporary bolt hole.
From there, the non-Banks family back story unfolds fairly rapidly. Jaff McCready turns out to be a very nasty piece of work indeed, with connections to criminals who aren't inclined to take things lightly, particularly when Jaff's gone missing with cash and drugs belonging to them after failing to dispose of a gun with the boss' fingerprints on the magazine.
Annie Cabbot, having offered to water Banks' pot plants while he's away but preoccupied with work matters, turns up at the cottage, gets shot for her trouble and is fighting for her life when Banks arrives back at Heathrow to be whisked aside by Dirty Dick Burgess at Immigration and updated about recent events.
Thrust into the middle of complicated, separate but intertwined cases, Banks needs to negotiate his way through developing events, something that isn't going to be a cakewalk, given the presence of a Professional Standards investigation into the death of his former neighbour.
It works out in the end, of course. It always does.
But the way it works out leaves Robinson with interesting possibilities for whatever comes next, given the significant physical and psychological scarring that's bound to have affected those who've got too close to this particular Bad Boy and his associates.
Another well-crafted cracker in an excellent series.