``We've got five major cases so far,'' announces Lt. Joe Gunther two-thirds through this tangled novel, and there's no doubt that Brattleboro's homicide squad is stretched to its limit. First, there's the murder of teenaged runaway Shawna Davis, doped to the gills for the week before she was finally killed. Second, there's the disappearance of angry Mary Wallis, the homeless advocate who took Shawna in shortly before she died. Third, homeless Milo Douglas turns up dead, not of the seizure everybody assumes, but of rabies. All three cases are probably tied to the fourth--the devious return to life of an imperiled, sinister convention center whose most ardent supporters, the leaders of Brattleboro, make Joe wonder just who he can trust in his hometown. But what does any of them have to do with the fifth--the strangling of unpleasant old Adele Sawyer only months before she was expected to die under her own steam (of which she had plenty)? From interrogations to forensics to the occasional car chase, Joe and his squad shine in unearthing the buried connections that hold the complex plot together--but their big break will depend on jogging the memory of a witness to the Sawyer killing whose mind is still trapped back in WW II. Joe's intricate seventh case is as far-reaching as his outsized sixth (The Dark Root, 1995, etc.), but so much more close-knit--every new suspect seems to awaken painful memories for Joe--that Mayor's Brattleboro ends by containing a whole sorry world.