So Shall You Reap (Guido Brunetti Series #32) by Donna Leon

On a cold November evening, Guido Brunetti and Paola are up late when a call from his colleague Ispettore Vianello arrives, alerting the Commissario that a hand has been seen in one of Venice's canals.

The body is soon found, and Brunetti is assigned to investigate the murder of an undocumented Sri Lankan immigrant. Because no official record of the man's presence in Venice exists, Brunetti is forced to use the city's far richer sources of information: gossip and the memories of people who knew the victim.

Curiously, he had been living in a garden house on the grounds of a palazzo owned by a university professor, in which Brunetti discovers books revealing the victim's interest in Buddhism, the revolutionary Tamil Tigers, and the last crop of Italian political terrorists, active in the 1980s.

As the investigation expands, Brunetti, Vianello, Commissario Griffoni, and Signorina Elettra each assemble pieces of a puzzle-random information about real estate and land use, books, university friendships-that appear to have little in common.

Until Brunetti stumbles over something that transports him back to his own student days, causing him to reflect on lost ideals and the errors of youth, on Italian politics and history, and on the accidents that sometimes lead to revelation.