While on the air, Frasier receives a phone call from Gretchen, who fears that her fencing instructor husband Gunnar is having an affair with a wealthy new client. Roz offers Gretchen a “sure-fire” way of determining if her husband is cheating: offer him a fattening meal or a diet plate. If he chooses the diet plate, it means Gunnar is trying to keep in shape for another woman.

Later that evening, Niles tells Frasier that Maris has a new passion: fencing. He explains how convenient it is for Maris to be able to practice her German, since her instructor does not speak a word of English. To his horror, Frasier realizes that Gretchen’s husband is having an affair with Niles’s wife!

The next day, Gretchen calls again, distraught because Gunnar chose the diet plate. When Frasier mentions his conversation with Niles, Roz persuades Frasier to confront Maris. Unfortunately, a mix-up causes Frasier to spill the beans to Niles, who is devastated. Niles challenges Gunnar to a duel, but with the language barrier, Gunnar winds up thinking that Frasier is in love with his wife, and challenges him to a duel instead.