This scene is pure Pulman. Graves has Sejanus catch up with Martina hidden by Claudius at a merchant's house in Brindisi. Pulman concocts this meeting between experts so his two poisoners can compare notes and discuss Caligula's role as parricide- none of which is supported by the sources. In Tacitus, Martina is found dead in Brundisium with a vial of poison in her hair and no evidence of suicide. This occurs before Piso even returns to Rome.