Before dawn, Duke Leto returns from his command post exhausted and reads an unsigned note delivered by a Fremen messenger: “A column of smoke by day, a pillar of fire by night.” Unsure of its meaning, Leto pockets the message for Hawat and decides he must stop excluding Jessica from his confidence after the damage caused by suspicion and Duncan Idaho’s accusation.

On the way to the family wing, Leto hears a strange mewling from the service passage. Armed but wary of activating his shield because of the captured lasguns, Leto investigates and finds the smuggler Tuek dead on the floor with a fresh wound. The sound leads Leto toward the house’s shield generator room, where Mapes lies dying from a stab in the back.

Mapes gasps fragments of warning about a killed guard, Tuek, escape, Jessica, and Leto, but dies before Leto can understand the full message. As Leto rises, a dart strikes him and paralyzes him. Yueh emerges from the generator room, revealing that the house shields have been sabotaged and the Atreides are exposed.

Yueh explains that he has betrayed Leto because he made a bargain with Baron Harkonnen and wants the Baron dead. Yueh plans to replace one of Leto’s teeth with a poison-gas capsule that Leto can release when brought close to the Baron, trusting that the Baron will gloat over his captive Duke. Yueh admits Leto is already doomed but offers Leto a reason to cooperate: Yueh claims he will save Paul and Jessica by making them appear dead and hiding them among people who hate the Harkonnens.

As Leto loses sensation and consciousness, Yueh removes the ducal signet ring for Paul and implants the deadly tooth. Yueh’s last command to Leto is to remember the tooth, turning the betrayed Duke into a final weapon against the Baron.