Travener stretched out his hand towards the bed, as if he were about to drop the knife on it. As soon as the hand that held the weapon shifted from the handle to blade and begin to lift, it's motion obviously designed to bring the knife above Travener's head and into a throwing position, Ian's finger closed over the trigger.
Doyle Travener deserved to die. It was the only way out for Annie. The only way out for either of them. The threat of the knife was the impetus Ian had needed to allow him to put an end to this.
Before he could complete the motion his finger had begun, Annie moved. She jerked away from the hold of his damaged arm and threw herself in front of him, positioning her body between his and the knife Travener held.
Distracted, Ian delayed a fraction of a second too long. Only when the firelight, glinting off the movement of the blade, drew his attention back to Travener did he fire.