A Surfeit of Guns (1997)

Sir Robert Carey took up his northern post as Warden of the West March in order to escape the complications of creditors and court life. Trouble, however, is where the dashing Carey, possibly a cousin of the Queen, finds it.
One black night in 1592, Carey is on night patrol along the unsettled border anchored by the garrison in Carlisle. It's a disaster. First, there's the fugitive he has to hand over to the warring Scots. Next come Wee Colin Elliot's sheep stealers. And then a gun explodes and takes off the hand of one of Carey's men. Back in Carlisle, Carey soon learns more faulty guns lie in the armoury in place of the sound weapons shipped in from Newcastle only last week. When these explosive deathtraps are stolen, he sets off in pursuit of both batches of guns--and the thieves.
The search ends in Dumfries where King James VI of Scotland--potentially King James I of England when his cousin Elizabeth dies--and his raucous court have assembled. James is as dissolute as ever, lovely Lady Elizabeth Widdrington, Carey's true love, is still shackled to her husband, and seductive Signora Bonnetti takes a serious interest in Carey and in the missing guns. Will the frustrated courtier be gallant enough to flirt with the Signora--and with treason?...
As wild as the American West, P.F. Chisholm's witty historical detections are also elegantly crafted and historically accurate as they reimagine the life of a real Elizabethan gunslinger. Her other Carey novels are A Plague of Angels (Introduction by Diana Gabaldon), A Famine of Horses (Introduction by Sharon Kay Penman), A Season of Knives (Introduction by Dana Stabenow). The author is at work on a fifth Sir Robert Carey.