Paw and order : a Chet and Bernie mystery / by Spencer Quinn.

Enhanced descriptions from Syndetics:

In the seventh book in the brilliant New York Times bestselling mystery series, canine narrator Chet and P.I. Bernie Little journey to Washington, DC, and the dog-eat-dog world of our nation's capital.
Stephen King has called Chet a canine Sam Spade full of joie de vivre. Robert B. Parker dubbed Spencer Quinn's writing major league prose. Now the beloved team returns in another suspenseful novel that finds Chet sniffing around the capital city and using his street smarts to uncover a devilish plot.
Chet and Bernie pay a visit to Bernie's girlfriend, Suzie Sanchez, an ace reporter living in far-off Washington, DC. She's working on a big story she can't talk about, but when her source, a mysterious Brit with possible intelligence connections, runs into trouble of the worst kind, Bernie suddenly finds himself under arrest.
Meanwhile Chet gets to know a powerful DC operative who may or may not have the goods on an ambitious politician. Soon Chet and Bernie are sucked into an international conspiracy, battling unfamiliar forces under the blinking red eyes of a strange bird that Chet notices from the get-go but seems to have slipped by everybody else. Most menacing of all is Barnum, a guinea pig with the fate of the nation in his tiny paws.
As Harry Truman famously quipped, If you want a friend in Washington, get a dog. Too bad he didn't get to meet Chet