In Chabon's alternate version of history, a piece of what was still the Alaska Territory was designated as a refuge for European Jews; the District of Sitka took in even more people in 1948, with the (fictional) failure of the nation of Israel. The novel is set in the present, as Sitka is about to revert to Alaskan control and its Jewish population is to be dispersed throughout the world. Many people aren't sure where they're going, since so many countries are still reluctant to admit Jewish immigrants.
Against this backdrop, police inspector Meyer Landsman finds his life falling apart. He has no real plans for life after Reversion; he's separated from his wife and living in a fleabag motel; he and his partner (who is also his cousin) have the highest rate of unsolved murders on the force. And now a bum has been found murdered in Landsman's hotel, the only clue to his identity his book of chess puzzles.
The setup is terrific, and Chabon's Sitka is a beautifully detailed creation. But around the midpoint of the book, the answers to the murder mystery begin to be revealed, and they just aren't that interesting. The last third of the book is heavy slogging indeed; the novel, which had gotten off to such a fine start, winds up a serious disappointment.