The Secrets of Vesuvius by Caroline Lawrence
It's the summer of AD 79, and Flavia Gemina the sea captain's daughter and her friends Jonathan the Jewish boy, Nubia the African slave-girl and Lupus the homeless beggar-boy set sail for the Bay of Naples, to stay with Flavia's uncle near Pompeii. They are soon absorbing in trying to solve a riddle that may lead to treasure. But then tragedy strikes - Mount Vesuvius erupts and the children are fleeing for their lives, in one of the worst natural disasters ever recorded. Not just a mystery - an absolutely thrilling action adventure that makes you feel you were there!