"A Poison That Leaves No Trace" by Sue Grafton

Kinsey and Me: Stories, G.P. Putnam's Sons, 2013, p. 127-146

The pioneering and prolific author of the Kinsey Millhone P.I. series died December 28, 2017 aged 77. First appearing in Sisters in Crime 2 (Berkley, 1990), "A Poison That Leaves No Trace" was one of her favorites, reprinted in at least two later anthologies at her request.

After giving the impression she thought Kinsey would be a man and suggesting her fee of $30 an hour is too steep, Shirese "Sis" Dunaway hires Kinsey to investigate her estranged sister Marge's death. Not believing the official finding Marge's death was without foul play heart-related, Sis casts suspicion on Marge's daughter, Justine.

Confirming the official finding with the hall of records and the funeral director, Kinsey then visits Justine on the pretense of owing Marge $600. Justine's eagerness to claim the money makes Kinsey suspect she's lying about something.

When you get to the twist that Sis and Justine both lie to Kinsey, you have to admire how convincing Sis is, her skepticism teasing out Kinsey's desire to prove herself.