This narrative device shifts the tension. The audience is no longer wondering who killed Harlan, but rather, will Marta get away with it? This twist transforms the film from a passive guessing game into an active thriller, rooting the audience’s sympathies in the "suspect" rather than the detective.
However, Johnson quickly subverts the traditional structure. In a conventional Agatha Christie adaptation, the detective interviews suspects, and the audience waits for the final reveal. "Knives Out" flips the script by revealing the "how" of the mystery early on. We see Harlan’s nurse, Marta Cabrera (Ana de Armas), accidentally administering a lethal overdose of morphine. In a panic, Harlan orchestrates his own death to protect her from police suspicion, constructing an elaborate ruse to give her an alibi.