"The Duke of Marylebone" tells the story of Rupert Siskin, a humble food taster from London who enjoys his slow-paced lifestyle, but his serious girlfriend, Lisa, has finally had enough. Claiming to need more adventure in her life, Lisa pushes to break up with monotonous Rupert. That is, until Rupert makes all the wrong changes to become Lisa's dangerous Mr. Right. But, when nothing goes as planned, Rupert turns to his only remaining option: politics, where perfectly legal thieves are created right in front of us.