Deep Freeze by John Sandford
Class reunions: a time for memories--good, bad, and, as Virgil Flowers is about to find out, deadly... Virgil knows the town of Trippton, Minnesota, a little too well. A few years back, he investigated the corrupt--and as it turned out, homicidal--local school board, and now the town's back in view with more alarming news: A woman's been found dead, frozen in a block of ice. There's a possibility that it might be connected to a high school class of twenty years ago that has a mid-winter reunion