Strong Poison is a 1930 mystery novel by Dorothy L. Sayers, her fifth featuring Lord Peter Wimsey and the first in which Harriet Vane appears.

The novel opens with mystery author Harriet Vane on trial for the murder of her former lover, Phillip Boyes: a writer with strong views on atheism, anarchy, and free love.

Returning from a holiday in North Wales in better health, Boyes had dined with his cousin, the solicitor Norman Urquhart, before going to Harriet's flat to discuss reconciliation, where he had accepted a cup of coffee.

Lord Peter Wimsey visits Harriet in prison, declares his conviction of her innocence and promises to catch the real murderer.

Wimsey suspects that to be a lie, and sends his enquiry agent Miss Climpson to get hold of Rosanna's original will, which she does in a comic scene exposing the practices of fraudulent mediums.

Housman's A Shropshire Lad, in which the poet likens the reading of serious poetry to King Mithridates' self-immunization against poisons, Wimsey suddenly understands what had happened.

Although Boyes and Urquhart had shared the dish, the latter had been unaffected as he had carefully built up his own immunity beforehand by taking small doses of the poison over a long period.

Freddy Arbuthnot, Wimsey's friend and stock market contact, marries Rachel Levy, the daughter of the murder victim in Whose Body?

[5] It has been adapted for radio three times: While Sayers was working on her first novel, Whose Body?, she began a relationship with John Cournos, a writer of Russian-Jewish background.