Blackout. The Erin O'Reilly Mysteries, #17

Who you are in the dark is who you really are A night you can't remember was either a really good night or a really bad one. When Erin O'Reilly wakes up in a notorious womanizer's apartment with a hangover, a new tattoo, and a gap in her memory, she has the feeling she had one of the bad ones. But it turns out New York had a worse night than she did. A power outage in a city is a dangerous thing, between looting, traffic accidents, and interrupted emergency services.
Somebody has tampered with Manhattan's power grid, plunging the city into darkness. Is it a reckless prank gone wrong? Or something much worse? An unexpected lead arrives in the form of a young man who walks into the Major Crimes office and confesses to a brutal murder. There's only one problem; the NYPD can find no evidence the crime took place. Erin will have to rely on her K-9 Rolf to untangle the truth behind a psychopath's scheme.
After all, a dog's nose doesn't need light to point the way.