Caligula, the young heir to the throne of the syphilis-ridden, half-mad Emperor Tiberius, thinks he has received a bad omen after a blackbird flies into his room early one morning. Shortly afterward, Macro, the head of the Praetorian Guard, appears to tell the Caligula that Tiberus, his great uncle, demands that he report at once to the Island of Capri, where the Emperor has been residing for a number of years with Nerva, his close friend; Claudius, a dim-witted relative; and Caligula's younger stepbrother Gemellus. Fearing assassination, Caligula is afraid to leave, but his beloved sister and lover Drusilla convinces him to go.