A sinister group of gladiators has come to Ostia and Nubia believes her missing brother may be amongst them. The children smuggle themselves into the arena to find him, till Lupus is caught and put with a wild beast and Jonathan faces the strongest gladiator in single combat. There is a deadly mystery here - but can they solve it in time?
Today is the day of the gladiatorial contest and Jonathan believes he's facing certain death. Flavia has disguised herself as a dancing girl, but that isn't a safe option when there's a big political conspiracy going on and the children have become part of it. Can they save the life of the Emperor's brother Domitian?
Lupus narrowly escapes kidnap by slavers on the streets of Ostia, but his friend Porcius and other children are snatched. Flavia and her friends sail after the slave traders. But they have a traitor right there on board with them and no one knows who it is. And their quest is threatened by a terrible storm.
In Rhodes, the children find the whole island is paralyzed by fear of Magnus, the mythical figure who master-minds the slave trade. There are rumors that he is a giant. The only way to save the kidnapped children is to get right inside Magnus' palace and to get evidence of his evil. In the end, Lupus has to tackle Magnus and his henchman alone.
In the darkness, Flavia and Nubia wake to cries and the sounds of a struggle. Flavia's father, has been stabbed and his life hangs in the balance. Only Nubia has faith that the gentle Aristo, their tutor, could not possibly be behind the attack. The children take a carruca into the hills outside Ostia, in pursuit of the murderer. But the murderer is willing to kill again...
Flavia and her friends are trying to save Hepsibah, a young Jewish midwife, wrongly accused of terrible crimes. Miriam is determined to protect her friend, who will deliver the babies she is expecting. Jonathan has a prophetic dream that someone will die. But who? This is one of Flavia's most difficult mysteries.
Hepsibah is now charged with two murders and her court-case is going disastrously wrong, as Flavia's choice of lawyer is young and inexperienced. Nubia, Lupus, Flavia and Jonathan have to race against the clock to find the evidence that will clear Hepsibah. Meanwhile, the comical drunken Floridius befriends Lupus and does his daft best to help out. Jonathan's prophecy of a death comes tragically true.