One day the fabulously wealthy Sir Guy Grand who is Peter Sellers with a much larger nose finds a young orphan kid in a park. On the spur of the moment he adopts young Ringo Starr, probably because Ringo has a well known honker in real life and Sellers sees something of himself in Ringo.
The idea is that Sellers has to have someone not just to leave his money to, but someone to impart his accumulated wisdom of the years which is boiled up into one single thought; that EVERYBODY has his price.
The rest of the film is a Monty Pythonesque group of skits in which Sellers tries to prove just that to Starr. They range from Laurence Harvey doing a striptease while doing Hamlet's soliloquy to a beat cop eating a parking ticket for 500 pounds. The title The Magic Christian refers to a Titanic like cruise ship that only caters to the upper crust. Sellers and Starr integrate that ship's maiden voyage in a most interesting fashion.
That the film is like Monty Python is no accident with Graham Chapman and John Cleese doing the writing. Ringo's former Beatle companero, Paul McCartney wrote The Magic Christian theme, Come and Get It which sums up the philosophy of the film.
After almost 40 years, The Magic Christian is acidly funny, but a still unsettling.