The fifth in the author's Georgian-period Jeweled Men series, those flounced and pomaded adventures in which a group of young gentlemen slashes one league farther in proving the existence of a traitorous plot against the ruling House of Hanover. Of course, romance weighs heavily as a heroine aids and abets. Here the bright, bumptious young thing is country-bred Zoe Grainger, sent by her weak Papa to stay in London with the odious Lady Buttershaw, she with the voice of a French horn and the civility of a mud hen. Zoe is to attend the Lady's fragile, invalid sister, Lady Julia. In the meantime Lady Buttershaw has arranged for Zoe to be squired around town by hot-tempered, lame Lieutenant Peregrine Cranford--chum, as it turns out, of other heroic chaps met in the earlier adventures. Typically, the romance has a rocky start, but, as mystery piles on mystery, the pair soon work as a team. Events touching Zoe and Peregrine have much to do with the search for Zoe's absent brother, Travis, a diplomat who carries a damning, treasonous ``Agreement'' forged by the ``League of Jeweled Men'' that names names. Brave Zoe spies, and brave Peregrine (and some friends) gallop to the rescue. Peril pops up at the mansion of Lady Buttershaw as urgent messages fly, and there are pistol- packing confrontations between all sorts of nefarious and noble studs. Of course there's that essential happy conclusion to the romance, as Peregrine quotes the Bard. One of Veryan's vintage best--pleasantly predictable, with agreeable people, gentle humor, and the fillip of a popular, sanitized version of 18th-century dialogue.