The Legend of Beka Cooper #2: Bloodhound book by Tamora Pierce

Beka Cooper is no longer a Puppy. She's a Dog now - a full-fledged member of the Provost's Guard, which keeps the peace in Corus's streets. Beka's natural skills of observation and tenacity are augmented by her unusual magical talents, which allow her to gather information both from pigeons are from the eddies of dirt and dust that swirl on street corners. But even her magic isn't very useful when unrest comes to Tortall's capital in the form of counterfeit coins, which turn up in shops all over the city. Merchants raise prices to cover their losses, and with winter coming on, hikes in food and fuel costs could spell disaster - most of all for the city's poor.

The Dogs discover that gamblers are bringing the counterfeits from Port Caynn - and that the Port Caynn Dogs don't seem to be doing anything about it. Beka and her mentor, Clary Goodwin, are chosen to go undercover in Port Caynn and find out what they can. And wherever Beka goes, so do some of her animals. Departing from Corus with her are the scent hound Achoo, who has been newly assigned to Beka, and the pigeon Slapper, who carries the voices of the dead.

In Port Caynn, Beka and Goodwin delve deep into the gambling world. There Beka meets a charming bank courier, who may be involved in the counterfeiting ring. Things come to a head just as Goodwin returns home to report in Corus. It won't be enough to Beka to be her usual "terrier" self. She'll have to learn from Achoo to sniff out the criminals - to be a bloodhound.