After his defeat at the hands of Batman in the previous volume, Deathstroke finds himself incarcerated...in Arkham Asylum? But it's not the Arkham he's used to - no, this one is run by the inmates, for the inmates, and as Slade's already tenuous link to reality frays even further, Hugo Strange and the rest of Gotham's villains threaten to warp his mind beyond repair. Plus, on the outside, Rose and Joey deal with their father's absence in the only way they know how - by fighting.
This is a weird one. Probably the weirdest arc of Priest's Deathstroke so far. There are more than few points where I wasn't sure what was real and what wasn't, which I guess is the point since neither is Slade. It gets a bit muddled, and Priest's unapologetic plotting does get a bit murky (to it's detriment this time around, unfortunately).
That said, the idea is sound, and he uses all of the characters you'd expect to see in interesting ways - Two-Face's role in the proceedings is surprising, definitely. Fernando Pasarin pencils most of these issues with his usual clean lines and solid-looking characters; I'd love to see him on more regular books again.
Aside from that, there's not much else to say. You know what to expect with Deathstroke by now, which is why I find it weird that DC are billing this as a one-off mini-series or something, when it most definitely isn't, and the context of all that came before it is basically necessary to understand anything more than the most basic plot.