Wondering who his biological father really is, Homer goes to the library to look in "Lifeguards of Springfield in the Twentieth Century." The only person in there whose name begins with M is Mason Fairbanks. Homer goes to his house posing a reporter, but eventually tells him he thinks he is his father, and Mason is delighted. He takes the Simpson family on a ride on his ship and tells them the story of the lost emerald treasure of Piso Mojado, which impresses them. However, when they come home, Grampa angrily accuses Mason of having tried to steal his wife and now trying to steal his family, and is saddened Homer would even think that Mason could be his real father. They have a DNA test, and after a suspenseful wait, Homer is thrilled to learn his real father is Mason Fairbanks.