They detail the adventures of four children who solve mysteries and have adventures in Ostia Antica, Rome, Greece, and beyond: Flavia, a rich Roman girl who lives in Ostia; Nubia, a freed slave girl from Africa; Jonathan, a rich Jewish boy; and Lupus, an orphaned mute beggar boy.

In 2008 a sequel trilogy for young adults was proposed, with the main characters being Jonathan's 14-year-old orphaned twin nephews.

On her blog and website, Caroline Lawrence has said the content was deemed "too edgy" for the Roman Mysteries brand and as a result has been put on hold indefinitely.

[citation needed] In April 2010, author Caroline Lawrence announced that she is planning a spinoff for younger readers.

[citation needed] Each of the novels has at least one map of the area covered in the story, sometimes also plans or diagrams; these are by Richard Russell Lawrence.