Stealing the Elf-King's Roses — Diane Duane

The highly acclaimed creator of many brilliantly realized worlds in fantasy and science fiction, New York Times bestselling author Diane Duane now presents a startlingly original new adventure--a gripping mystery that spans seven alternate universes...

THE CASE OF THE ELF KILLERS
Los Angeles prosecutor, sleuth, and forensic lanthanomancer Lee Enfield relies on her mystic Sight to gather the truth from suspects and crime scenes. But when she investigates the shooting death of an Alfen media exec, her powers, like those of her fayhound partner Gelert, uncover only deeper mysteries. The murder is revealed to be part of a deadly plot against Elves, and mounting evidence implicates the highest members of the Alfheim government...including the Elf-King himself. Now, to determine the truth, Lee and Gelert must secretly infiltrate Alfheim, a universe forbidden to mortals--and crack the case before an inter- dimensional war destroys all creation...