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?

It's the feast of Saturnalia when all the world's turned upside down with dancing and feasting and mis-rule. An abandoned ship has washed up in Ostia - carrying ghosts or monsters or who knows what. And Flavia has another challenge when her father brings home a horrible woman he wants to marry.

Nubia tracks down the monster that escaped from the ship - and discovers there's more than one monster and nothing is what it seems. Flavia's battle to expose her father's new fiancee as a murderer gets her into deep trouble and finally, comes close to costing her life and the love of her friends.

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...

As the children close in on the man they are pursuing, they are led into a trap from which they are unlikely to escape alive. Their only hope is that Lupus can bring them help. They must catch the man who tried to kill Flavia's father before he can strike again. Who is the mysterious attacker?

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.