The secret service - Wendy Walker

First published in 1992, Wendy Walker's The Secret Service takes place in an alternative 19th century.

A young king sits on the English throne and is about to take a bride.

His Majesty's Secret Service has learned of a plot against the royal couple: three nobles from the Continent, all passionate connoisseurs of the arts, are ready to release their dastardly attack in an effort to topple the current dynasty.

The agents of the Secret Service, apprised of the threat, have formulated a technology that enables them to masquerade as objects-the objects most desired by the connoisseurs-in order to spy upon them undetected.

Thus Polly, the protagonist, is sent abroad as a crystal goblet, while her two male colleagues perform their missions as a rose bush and a bronze statue of Thisbe.

Once on the mainland, they discover, to their great peril, the full scope of the villains' designs.