When fictional sleuths from different series join forces, the effect is usually shallow and gimmicky--as in the many recent collaborations of Bill Pronzini, for instance. Here, however, Hillerman brings together his two series characters--middle-aged, cynical Lieut. Joe Leaphorn and young, mystical Officer Jim Chee--without in any way diminishing the stark power and somber integrity that have distinguished previous exploits of the Navajo Tribal Police. While Leaphorn is brooding about the three unsolved homicides in his district, an unknown assassin tries to kill Officer Chee some distance away. And the coincidence (or is it?) brings the two lawmen together, though at first Leaphorn is severely skeptical about Chee--because cops who get shot at are usually corrupt, because Chee's spiritual bent alienates the older, more worldly policeman. (There have even been complaints about Chee's shaman-izing--from the selfless doctor who heads a highly effective local clinic, mixing medicine with some pseudo-mysticism.) It soon becomes clear, however, that Chee's mystical knowledge is crucial to the investigation--since all the murder-victims turn out to be linked (in rumor, at least) to Indian witchcraft, to the fearsome practice of "skin-walking." And, before the very earthbound motive behind all the mayhem is revealed (not too hard to guess), Chee's tribal ambitions lead him into a near-fatal trap. . .while Leaphorn's concern over his wife's health (does she have Alzheimer's disease?) compounds his discomfort with the science/faith issues in the murder case. Haunting backgrounds, quietly disturbing incidents, tautly orchestrated tensions: another indelible Navajo-world imprint from the author of The Ghostway and People of Darkness.