Wendy recognizes the knife-wielding intruder as Marybeth, her husband’s secretary and Russell Simonds’s wife, standing near Russell’s corpse with a bloodstained trench coat. Marybeth orders Wendy to sit at the kitchen table and interrogates her about the ten-month affair with Russell, framing it as the moment her marriage fell apart.

Marybeth then accuses Wendy of killing Douglas Garrick with Russell. Realizing denial is pointless, Wendy admits she killed Doug, and Marybeth erupts, calling Doug “the best” and blaming Wendy for his death. Wendy tries to stay calm and looks for a chance to disarm Marybeth, but Marybeth keeps control with the knife.

Marybeth demands Wendy write a confession describing the affair and a conspiracy to murder Douglas. Under threat, Wendy writes what Marybeth wants, including that Wendy “can no longer live with the guilt” and has decided to “take both our lives,” then signs her name. Wendy understands the confession is meant to stage the night as a murder-suicide.

Overwhelmed and panicking, Wendy vomits at the sink and begs Marybeth not to kill her, arguing that a stabbing would not look like suicide. Marybeth agrees—but only because she has chosen a different method.

Marybeth explains digoxin toxicity and reveals Wendy has already ingested it through the pinot noir. As Wendy develops cramps, dizziness, and blurred vision, she collapses and pleads to be taken to a hospital. Marybeth refuses, promising Wendy a slow, painful death as revenge for Douglas.