Tangled Up in Blue by Joan D. Vinge

From the publisher (source: The Internet Book List):
They call the city Carbuncle because it is both jewel and fester: the personal playground of the Snow Queen, it's also the place where the high and mighty get their water-of-life youth serum. But it's just become Hell for Hegemonic Police Officer Nyx LaisTree.

Tree lost more than simply a lot of blood on the night he and some other off-duty cops raided a warehouse full of contraband - illegal tech the Snow Queen herself covets. He also lost his partner, his badge, and even his memory of what went wrong. Something terrible happened that night, but nobody's talking since the raid went bad. Now eveyrone Tree trusted is dead, and he's a marked man, wanted by the underworld, by the Snow Queen's agents, by dirty cops...and maybe by others even worse.

His only hope rests with a by-the-book sergeant named Gundhalinu who happens to hate his guts, and a ravishing shape shifter whose loyalties are as elusive as her true face. As the maze of deceit and danger leads them deeper into Carbuncle's twisted heart, they realize that not only their lives are hanging in the balance, but possibly the fate of the Hegemony itself...

This book is part of the "The Snow Queen Cycle" series.
Here are some other books from this series: