Evelyn Howard is the secondary antagonist of Agatha Christie 1920 novel, The Mysterious Affair at Styles, which was her first published novel and the debut of Hercule Poirot. She is the lover and accomplice of Alfred Inglethorp, assisting him to murder her companion, Emily Inglethorp, and frame John Cavendish. Originally, she was shown as a firm detractor of Alfred, but their relationship was revealed in the plot twist.
She was portrayed by Joanna McCallum in the 1990 television film adaptation from Agatha Christie's Poirot, and was voiced by Nichola McAuliffe in the 2005 radio adaptation of BBC 4 Radio.
Ms. Evelyn Howard was the companion of Emily Inglethrop, the owner of Styles, and was apparently showing disgust and objection towards Emily's husband Alfred. However, it was revealed that Evelyn was Alfred's lover in secret and planned to poison Emily in order to take over her fortune.
After Emily discovered that her eldest stepson, John Cavendish, had a love affair, she began a fiery arguement with him and changed her will. However, she later discovered that Alfred had a love affair with Evelyn as well and was distressed at night, learning of their attention. Unknown to her, however, that the pair already added bromide to Emily's regular sleeping medicine, which contained strychnine. The bromide made the dose of sleeping powder lethal, killing Emily later.
Afterwards, Evelyn forged John's handwriting and framed him for the crime as well as the person who obtained the poison. Meanwhile, Alfred intentionally had himself into the custody in order to throw away suspicions. However, his intention of hiding the letter between him and Evelyn failed after Poirot discovered the said letter after a remark from Hastings, solving the case.