A Sea of Troubles takes place on the island of Pellestrina, one of the 2 barrier islands that enclose the lagoon of Venice. Two fishermen are murdered and their boat blown up, and none of the residents will give any information to the police. Signorina Elettra Zorzi has a cousin on the island and visits every summer, so she volunteers, against Brunetti's wishes, to go to the island to see if she can find out anything.
The investigation reveals that clamming in the Venice lagoon is lucrative, and that clammers incur the hatred of other fisherman, because they dredge the bottom leaving nothing behind.
This is one of the weaker of the Brunetti series. Leon tried to fill out the character of Elettra by taking her outside the office environment, but it just didn't work well.
For those of us who have read all the other books in the series, this one was interesting and not at all bad. For someone just starting the series, I would put this one low on the priority list.