The Pirates of Pompeii by Caroline Lawrence

It's late August, AD 79. The Roman world is reeling from the eruption of Mount Vesuvius. Volcanic ash covers the land, sunsets are blood-red and the sea gives up corpses of the dead.
 
At a makeshift camp south of Stabia, hundreds of refugees from the cities of Versuvius try to come to terms with the disaster. When children begin to go missing from the camp, Flavia Gemins and her friends Jonathan, Nubia nad Lupus investigate a powerful and charismatic man known as the Patron.
 
The third Roman Mystery leads the four friends on a dangerous mission where they encounter pirates, salve-dealers and death.
 
Suitable for ages 11-13 years old