Rome, AD 19–20. Tiberius, with Sejanus' help, is ruling with an iron fist. Only Germanicus is preventing total tyranny, but when he dies in Syria under mysterious circumstances, it is widely rumored that Tiberius is behind it. Germanicus' wife Agrippina accuses Piso, the governor of Syria, and his wife Plancina of murder and treason. At Claudius' suggestion, they are tried in the Senate, so as to avoid any backroom subversion of the courts by Tiberius' agents. Martina, the poisoner, is held in a secret location before the trial by Herod Agrippa and Claudius, but she is found by Livia's agents. She reveals to Livia that Germanicus' own son, Caligula, aided her in bringing about his death by convincing him that he had been cursed. Piso blackmails Livia and Tiberius with evidence that they approved of Germanicus' murder. Livia retaliates by threatening Plancina with Martina's testimony, but the incident is enough to cause a permanent rift in her relationship with Tiberius. Plancina attempts to convince Piso to commit suicide, knowing that she will be spared by such an outcome. When Piso has second thoughts, Plancina stabs him, bringing the trial to an end, and Agrippina and her friends have to be satisfied that at least "some justice" was done. Caligula, after being punished by Antonia for being found naked with his sister Drusilla, sets fire to the family home in retaliation, burning it to the ground.