Night Watch - Terry Pratchett

"Night Watch turns out to be an unexpectedly moving novel about sacrifice and responsibility, its final scenes leaving one near tears. . . Terry Pratchett may still be pegged as a comic novelist, but . . . he's a lot more." — Washington Post Book World
Getting knocked back in time thirty years, Sam Vines, Commander of the Ankh-Morpork City Watch experiences a day like no other in which past, present, and future collide with hilarious—and poignant—results in this rollicking Discworld adventure from Terry Pratchett.
One moment Commander of the City Watch Sam Vimes is chasing a murderer across the rooftops of Ankh-Morpork. The next, he's lying in the street below, naked—and back in his own tough past thanks to a lightning strike and a group of meddling, time-manipulating monks.
It's a dark Discworld that is all too familiar. Worse, the cop-killing psychopath he'd been pursuing has been transported back with him, and it's the eve of a deadly street rebellion that took a few good (and not so good) lives. Vimes is determined to do his duty— track down the murderer and change the outcome of the rebellion. By changing history he might just save some worthwhile necks, and steer a novice watchman straight—an impressionable young copper named Sam Vimes.
But if he succeeds, Sam knows it could cost him the future—including the job and the family he loves.
The Discworld novels can be read in any order but Night Watch is the sixth book in the City Watch series. The series includes:

Guards! Guards!

Men at Arms

Feet of Clay

Jingo

The Fifth Elephant

Night Watch

Thud!

Snuff