See Delphi and Die (Marcus Didius Falco 17)

Through his brother-in-law Aulus, Falco hears details of two young
Roman women who have died in Greece while seeing the sights of the
ancient world. Falco and his wife, Helena, travel to Greece to meet up
with the tour party which included one of the women, seeking clues to
her murder, passing through Olympia, Corinth, Delphi and the oracle of Trophonius at Lebadeia before finally arriving at Athens.

The wayward Aulus is playing truant in Greece where, instead of
studying law at Athens, he is investigating the death of Valeria
Ventidia, a newly married Roman girl at Olympia, as well as another
death which occurred three years ago around the same area. Falco's
mission has two objectives: to send Aulus back to school, and solve the
mystery behind the deaths at Olympia. Eventually, a connection between
the two deceased women is deduced: both had joined tours provided by
Seven Sights, a tour company of dubious reputation, currently operating
in Greece.

Falco's investigation does not go smoothly, however: the Roman
authorities are not interested in properly investigating the deaths
(much less governing Greece itself), and at Olympia Falco is attacked by
a potential suspect, who later turns up dead in suspicious
circumstances, the death blamed on Falco's ward Glaucus. Low on funds
and unwilling to be confronted by the angry locals, Falco and his
followers - Helena, Albia, Glaucus and Falco's nephews - are forced to
leave Olympia for Corinth but not before discovering that Valeria's
killer may have been connected to athletes who trained at Olympia.../...