Mr. Satterthwaite (christian names unknown) is an observer of life with an acute sensitivity to atmospheres, a keen eye for personalities and a gift for deduction. The last is catalysed by the presence and personality of his mysterious friend Mr. Harley Quin or 'Harlequin' allowing Mr. Satterthwaite to right or prevent wrongs.[1] He has also worked with the eminent Hercule Poirot.[2]
Mr. Satterthwaite is a bachelor - his only real romance ended abruptly when the lady confessed to him her passion for another man - well to do with no day job. He is a bit of snob, a connoisseur of the arts, and sentimental to the last degree with a special weakness for young lovers.
In Three Act Tragedy, Mr Satterthwaite is a guest at Sir Charles Cartwright's house party, where another guest dies suddenly. Sir Charles suspects that the man was murdered. When another man dies in similar circumstances, Mr Satterthwaite helps Sir Charles and Poirot investigate.
Portrayals 
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- Murder in Three Acts (1986 film) - Does not appear.
- Three Act Tragedy (BBC Radio 4 adaptation) - George Cole.
- Three Act Tragedy (Agatha Christie's Poirot episode) - Does not appear.
