Egghead, Olga, and the Cossacks steal two pounds of radium so they can hatch a 40-million-year-old Neosaurus egg and take over Gotham City.

After lifting the Queen's priceless collection of snuffboxes from a Londinium museum, Lord Marmaduk Ffogg and his sister, Lady Penelope Peasoup, escape unnoticed in thick fog which he creates with his large meerschaum pipe. Batman, Robin, and Batgirl are asked to help solve the robberies.