The revolver that Annie Walker (played by Piper Perabo) uses is a Chiappa Rhino 20DS.
The Rhino was introduced at the 2010 SHOT Show, where it drew the crowd because of its distinctive design. According to Amercan Rifleman it functions differently than it looks. The geometry of the design seems off because the trigger is positioned about mid-cylinder and the hammer is directly above—as opposed to forward of—the grip.
The six-shot Rhino is basically the same length—about 0.2 inches thicker and 1-inch taller—and 5.5 ounces heavier than the five-shot Model 36.
Annie Walker’s character is about a CIA operative with gorgeous girl-next-door looks and the instincts and intelligence of a gifted spy; she's described as a brilliant linguist with a thirst for adventure.
Of interest, new characters will be joining the cast of Covert Affairs season-four including Emma Fitzpatrick who plays Violet Hughes, an innocent college student who has familial ties to the spy world. Find out more at The Hollywood Reporter.