In times past, the subway was more like a bizarre amusement park ride than a safe, clean way to get from Fort Greene to Soho.

That smack got cleaned up, but Adam Mansbach, who wrote the brilliant children’s-book-for-adults, Go the F**k to Sleep, returns to NYC’s graffiti heyday — if only for a night — in his new adults’-book-for-adults, Rage Is Back.

The first half reads like the time-traveling, drug-muddled story it is. The picture comes together slowly as a biracial teenager named Dondi discovers a slit in the time-space continuum, marijuana turns everything a bit hazy, and the reader starts to make sense of a sprawling cast with names like Dengue Fever, Cloud 9, Amuse, Sabor, and, of course, Rage.

The second half gels in a most satisfying way as fractured relationships are mended and old friends hatch — and splendidly execute — a plan to exact careful revenge on the man who long ago split them apart.

Read it on the B train.

Available at amazon.com, $15. Launch events held tonight, 7 p.m., at The PowerHouse Arena, 37 Main Street, at Water Street, Dumbo (718-666-3049 or powerhousearena.com); and tomorrow, 7 p.m., at McNally Jackson, 52 Prince Street, between Lafayette and Mulberry Streets (212-274-1160 or mcnallyjackson.com).

Photo: Courtesy of The Viking Press