A pregnant Mary Malone does chores as she awaits the return of her policeman husband from work. When he arrives home, he is clearly in a bad mood and heads directly for the liquor bottle.
Mary tells her husband of their plans to meet with one of her friends for dinner, but noting her husband's mood she offers to cancel the plans and make dinner herself. As Mary heads to the garage to get meat out of the freezer, her husband Patrick stops her to have a serious discussion.
He tells her that he wants to leave her. Mary is shocked. Patrick tells her that he has fallen in love with another woman and wants a divorce. Mary is heartbroken, but insists that he stay for supper.
Mary slowly heads to the garage where she takes a frozen leg of lamb out of the freezer. She brings it into the kitchen and unwraps it. When she returns, Patrick is getting ready to leave. Before he can go she sneaks up behind him and hits him with the frozen leg of lamb and kills him. She takes the leg of lamb back into the kitchen and places it in the oven where she begins to cook it. When she is done, she nervously contemplates what she should do next. Suddenly an idea hits her. She increases the temperature in the oven and calls her friend Molly and cancels her dinner date. Mary grabs her coat and heads out the door. She goes to the supermarket and buys a bag of groceries. When she comes home, she throws the bag onto the ground. She throws some papers onto the floor and makes it look like there was a struggle in the house.
She then phones the police. A detective arrives and interviews Mary. She tells him that she arrived in the house and found Patrick dead. Photographers arrive and they begin to take pictures of the crime scene and dust for prints. The detective continues to interview Mary while a doctor arrives and begins to examine her husband's body.
The detective heads to the kitchen and notices the roast in the oven. Mary tells him that the roast was for dinner and that she headed to the grocery store for vegetables.
After examining the body, the doctor tells the detective that Patrick has a fractured skull. He was killed by a blow to the back of the head. The doctor, however, cannot only say that he was hit with a heavy blunt object, maybe a club.
After the doctor leaves, the detectives notices a number of clues in the crime scene: Patrick was wearing his coat when he was killed and he had a drink of straight whiskey with soda and ice.
The detective believes that Patrick was worried when he came through the door. Mary, however, sticks to her story and tells him that her husband was not acting unusually when he first came home.
The detective tells Mary that he does not believe that the murder was pre-meditated and that he does not think the murder was done by a professional. He tells her that the murder was probably a crime of passion that occurred after a quarrel. Believing this, the detective thinks that the murder weapon
is somewhere in the house. The detective asks Mary if there is anything missing in the house like a vase or a baseball bat.
The detective asks Mary to show him around the house so that he can find the murder weapon.
After, the search is over the detective tells his partner Mike that he believes that the crime scene was arranged after the murder took place. The detective notes that Patrick must have been hit on the back of the head since there was no marks of struggle on his body. Since Patrick was carrying a gun and did not draw it, the detective concludes that he must have been surprised.
Knowing that Patrick fooled around on his wife, the detective begins to believe that a woman probably killed him.
The detective notices that the oven is still on. He heads to the kitchen and takes the now-cooked leg of lamb out of the oven. Believing that whatever it is would be ruined, the detective is surprised to see that it is perfectly fine. It doesn't dawn on him that it took so long to cook because it was frozen.
Mary comes into the kitchen and offers the policemen coffee. Noting that she will have to throw the roast away if it is uneaten, she offers the detectives a lamb dinner.
Later, as the detectives and policemen are finishing the leg of lamb the they start to talk about the case and the missing murder weapon. Mike says that it is probably on the premises, and Jake notes that for all they know, it could be right under their noses. Hearing this, Mary lets out a little chuckle.