Will and Marcus are enjoying a friendly game of badminton over the hedge when Marcus breaks the mood by suggesting all three of them get a dog. Will does his best to explain he's not part of Marcus' family, which is when Marcus insists he will be when he marries Fiona. Marcus marches into Fiona's kitchen to correct the situation. She tells him not to worry; number one, she'd never date Will in a million years. And number two, as a mother, she doesn't date. This whole dad thing is Will's fault, and it's high time he starts acting more like a neighbor than a dad! Realizing Fiona has been celibate for 11 years, Will begs her to get laid.
After a yoga session, Fiona asks Dakota if it's weird that she hasn't had sex with anyone since Marcus' dad. Grabbing her phone, Dakota asks Fiona to list all the men she knows. Sadly, the only one that comes to mind is her plumber, aptly named Lou, who left his card the other day. Dakota dials and sticks the phone in Fiona's hand demanding she ask Lou for a date. And when Fiona predictably chickens out, Dakota attacks the sink, ripping out the sprayer. Now Fiona really does need a plumber!
Finding Will and Andy at the grill, Marcus asks to learn the ropes of grilling. Intent on setting boundaries, Will advises Marcus to ask Fiona to teach him, then refuses to play badminton. Dakota is on hand when Lou the plumber arrives, which is a good thing, because she has to walk Lou through asking for a date, and then she has to accept the invitation for Fiona. Later, Fiona broaches the subject of dating with Marcus, who assumes she's referring to Will. Displeased when Lou shows up to take Fiona to dinner, Marcus proclaims him merely a blip on the road to Willsville. Long years out of the dating game, Fiona is beyond awkward, and Lou doesn't really have a way with the ladies. Once they leave, Marcus rushes next door, where Will gets serious, insisting he will never like Fiona in "that way." This entails an explanation, which somewhat resembles the classic "sex talk," stunning Marcus into near-catatonia. The veil has been lifted... forcing Marcus onto his bicycle, pedaling maniacally towards the restaurant where Fiona and Lou are suffering through their date. Marcus runs into the restaurant screaming, "Don't you dare intercourse her!" Fiona is just asking where Marcus heard that word when Will runs in, hoping to bring Marcus home. The ensuing argument sends Lou packing.
Back at home, Fiona lays into Will for scooping the birds and bees conversation with Marcus, which is every parent's right - not a neighbor's rite. Will softens; the truth is he's attached to Marcus, and sometimes little dudes need the wisdom of big dudes. Fiona and Will decide to spell it out for Marcus: they're never getting married!