City of Gold and Shadows

A recent murder in Wales leads Detective Inspector Felse to the mysterious disappearance of an architect and a case dating back to ancient Rome.

When archaeologist Alan Morris disappears in Turkey, his great-niece, Charlotte, regrets never having gotten to know him better. In an attempt to better understand him, Charlotte begins reading the books he wrote. One of them leads her to visit the Roman site of Aurae Phiala on the Welsh border—the last place her great-uncle worked before leaving for Turkey. But when Charlotte arrives, she finds more than just a few old stones. . . .

First there is a charming young man, coincidentally staying at the same hotel, who is very insistent on being her guide. Then a troublesome schoolboy disappears and a corpse is found. Detective Chief Inspector George Felse is called in to solve a case with origins in ancient Rome.
 
City of Gold and Shadows is the 12th book in the Felse Investigations, but you may enjoy reading the series in any order.