The story is pitched as a free translation of the memoirs of Britannicus, serving for 25 years as the slave of Caligula, emperor of Rome from AD 37 to 41 who is historically known for being insane.

It treats a number of different supposed facets of Caligula's life, including his popular early acts as emperor and his descent into madness.

Britannicus watches as Caligula begins falsely accusing, fining and even killing individuals for the purpose of seizing their estates during a financial crisis caused by his own wasteful spending.

He levies taxes on lawsuits, marriage and prostitution, and begins auctioning the lives of the gladiators at shows.

The novel also includes the famous story that once, at some games at which he was presiding, he ordered his guards to throw an entire section of the crowd into the arena during intermission to be eaten by animals, because there were no criminals to be prosecuted and he was bored.