As
Marge drives on a highway, she finds a toll booth, but she and other
Springfield residents drive through an adjacent forest trail to avoid paying. A week later,
Mayor Quimby deploys tire spikes and blocks off the escape route. When Marge comes to the booth, she refuses to pay and backs up, blowing out many cars' tires, which are thrown into the Springfield tire fire. The heat and smoke from it melt ice on Mount Springfield and reveal a mailman frozen for forty years. One of his letters is delivered to
Homer's mother,
Mona. It is from her old lifeguard boyfriend, whose name begins with an M, who writes that if Mona replies to the letter, she has chosen him, and if she does not, she is choosing to stay with her husband,
Grampa, but he believes the baby she is carrying is his. Wondering who his biological father 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 as 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 invite Mason home for dinner, Grampa accuses him of having tried to steal his wife and now trying to steal his family and is saddened Homer would think that Mason could be his real father. They take a
DNA paternity test, and Homer is thrilled to learn his real father is Mason. Later, while Marge,
Bart,
Lisa and
Maggie have an awkward visit with Grampa, Mason and Homer are underwater in individual submarines salvaging the lost treasure. Homer gets separated from Mason, and he follows a small light from a glowing fish, thinking it is him, and gets stuck in coral. As his oxygen runs out and he loses consciousness, he sees flashbacks of himself and Grampa. After being rescued and spending three days in a coma, Homer wakes up in a hospital and says he considers Grampa to be his real father. Grampa reveals he switched the labels on the DNA samples after seeing how happy Homer was with Mason, and the duo share a hug. ==Production==