This is book 33 of the "Spenser" series.

This note contains spoilers for the book.

Couple of kids pull off a school shooting. Coveralls, gloves, two guns each (non-matching 9mm). And leave everything on the library tables before the cops get to them. Er, him; there were two kids, but one of them is missing when the cops get there.

And all the parents and lawyers and cops and prosecutors "know" those kids did it, and they both confess to doing it (after the one they caught fingers his friend), and nobody knows why, or where they got the guns, or how they learned to shoot, or anything. And nobody cares.

Well, except one grandmother, and Spenser.

So after beating up a few people and shooting one and killing another (in clear-cut self-defense, but he does end up feeling that if he'd beaten the guy up right, the guy wouldn't have tried to ambush him later) and having one valuable witness he'd intended to protect murdered on him, he eventually finds a sex abuse situation and a blackmail situation which between them are what really triggered the kids.

It's nice that Spenser and the cops realize that the kids had to have at least practiced, and probably had some training, to actually hit 17 out of 31 shots, or whatever the exact numbers were.