The Marathon conspiracy - Gary Corby

Nicolaos and his partner in investigation, the clever ex-priestess Diotima, have taken time out of their assignments to come home to get married. But if Nico was hoping they'd be able to get hitched without a hitch, he was overly optimistic. When they arrive in Athens, there's a problem waiting for them. The Sanctuary of Artemis is the ancient world's most famous school for girls. When one of the children is killed, apparently by a bear, and another girl disappears in the night, Diotima's childhood teacher asks her former pupil to help them.