Jon Arbuckle is going on a date with one of his girlfriends, until he thinks that she already has one, so he tells Garfield to hide his black book of women's phone numbers. After a misunderstanding, chaos ensues when Jon wants Garfield to give back the book.
Jon is singing in the shower about his new girlfriend Heather. While he is doing that, his answering machine picks up a message. Meanwhile, Garfield is feeling tortured from Jon's singing. As soon as Jon gets out of the shower, he checks the time and sees that it is 6:45. He goes to get his little black book of women's phone numbers and dials up Heather's number. The person who picks up is a man asking Jon why he is calling. Jon tells him that he is Heather's date for the night. The guy tells him that she is going to dinner with him and hangs up. Jon, dismayed over another guy at Heather's place, decides to swear off women for good and remain a bachelor.
Meanwhile, at Heather's apartment, Heather gets out of the shower and asks who was on the phone. The guy who answered is actually her brother Mike, who she met up with at the truck stop. Mike is wary about any man who wants to take Heather out on a date while Heather assures him Jon is alright. It is revealed that she was the one who left the message and she wonders why Jon had not received it.
Jon, now dressed casually, gives Garfield his book and insists that he not give it back to him no matter what. At first, he thinks that he could call another woman and asks Garfield to return the book. Each time Garfield tries to, Jon reminds him not to do it, then asks for it again. Frustrated, Garfield leaves the room. Just as Jon is about to order a pizza, he gets the message Heather left him and finds out that Mike was her brother and not another date. When Jon asks Garfield to bring his book back, Garfield, thinking Jon is still testing him, says it is hidden. Jon is determined to get his book back.
Jon makes Garfield a big lasagna (which Garfield calls medium-sized) in hopes that this will persuade Garfield into revealing where the book is. Garfield still refuses to tell, causing Jon to chase Garfield to get the answer out of him. Just as that goes on, Heather and Mike drive up to the house and find Jon attacking Garfield. Disgusted with Jon's actions on Garfield, Heather breaks up with Jon and Mike tells him to stay away from her. Just as they leave, Jon tries and fails to explain what happened. Garfield reveals that he hid the book in Jon's back pocket. Heartbroken, Jon tells Odie to bury the book in the backyard and apologizes to Garfield for the way he acted, resulting in the two bonding. When Heather returns to scold Jon again, she sees him and Garfield together; she forgives him and tells him she will be available tomorrow night. Elated, Jon tells Odie to return the book, only to find that Odie refuses to show him where he buried it.
Out in the backyard, Jon is digging it up looking for the exact spot Odie buried it in. Garfield and Odie wish Jon would make up his mind while Jon continues frantically looking for his book.