'Jack' in the story is Sergeant Jack Noonan, a police officer known to Mary Maloney as he worked alongside her husband Patrick. Jack is a foil to Patrick Maloney and Mary Maloney's characters. He is caring and compassionate towards Mary-
Dahl also uses some of Jack's dialogue to illustrate the irony of the investigation into the attack on Patrick Maloney-
“It’s the old story,” he said. “Get the weapon, and you’ve got the man.”
There is great irony in the fact that the officers keep overlooking the murder weapon as it is in the oven. Also, they are not looking for a man, as it is Mary who is guilty.
Mary uses Jack's sympathy for her to her advantage. She asks him to get her a drink, and convinces him to talk the other men in to eating the leg of lamb.
Jack's naivety concludes the scene of the investigation at the end of the story. The officers discuss the whereabouts of the murder weapon as they eat it-
“Probably right under our very noses. What you think, Jack?”
And in the other room, Mary Maloney began to giggle.