The next morning, Basil arrives to check on the hotel to see if everything is sound. However, he finds that, due to a misunderstanding of the plans, the builders have blocked up the dining room rather than the drawing room, much to his dismay. Moreover, there is now a door in front of the stairs rather than leading into the kitchen. In a combination of rage at the shoddy work and fear over his wife's anticipated reaction, Basil, after tripping over Sybil's gnome, furiously threatens first Polly and then Manuel, before phoning O'Reilly and threatening that if he is not at the hotel in twenty minutes to fix the problem, he will "come over there and insert a large garden gnome in you."
O'Reilly arrives, and while Basil is imploring him to get to work, Sybil - having forgotten her golf shoes - arrives back earlier than expected, spots O'Reilly's van and immediately becomes suspicious. Basil blames the chaos on Stubbs's men. Sybil (dangerously calm) responds to this by telling Basil that she saw O'Reilly's van outside. Basil explains this by saying O'Reilly has come in to fix up Stubbs's mess. Sybil, to Basil's surprise, actually agrees with him, but thinks that, since Stubbs made the mess, he should set it right as there would be no point in paying O'Reilly when Stubbs would have to do it for free. At that moment, Polly calls the front desk from another room impersonating Stubbs's secretary, but is caught by Sybil almost immediately and the game is up, as is Sybil's dander.
Sybil angrily confronts Basil for hiring O'Reilly and vows that she will make him regret it for the rest of his life. Basil continues his attempts to convince her it was "at least partly" Stubbs's fault, but Sybil orders him to halt his lies. Berating herself for letting Basil oversee the arrangements, Sybil assaults Basil, hurls the cash box across the room at him and goes into a furious tirade about all the times he'd hired O'Reilly to do jobs with shoddy, disastrous results. O'Reilly merrily appears and, upon admitting his mistakes, tries to joke about it. He even smiles at her when she's ranting, which terrifies Basil. This really sets Sybil off, as she has no capacity for a man smiling at her when she's angry unfortunately, and gives O'Reilly - and her husband - a harsh beating with an umbrella, and tells him to leave and never return. Sybil calls Stubbs to get him to do the work the next morning. She then storms off, not to return until that time. Unwilling to concede defeat, Basil convinces O'Reilly to stay and do the work anyway.
Sybil arrives in the morning to find the renovations have been completed by O'Reilly, apparently with no problems. As Stubbs arrives, Sybil finds herself in an embarrassing situation at having called on him, seemingly now for nothing. Stubbs looks over the renovations and admits at first that whoever did them did a very good job. Then, in further questioning Basil about the work, Stubbs finds out he was not called in for nought after all; while making a doorway leading into the kitchen, which was on a load-bearing wall , O'Reilly had used a wooden lintel for the support frame rather than a concrete one or Rolled Steel Joist. The supporting wall could give way at any moment, and he will need to repair it immediately, before the building collapses. As Stubbs almost frantically telephones his men to come over and help with this job, Basil leaves and marches down the driveway with Sybil's garden gnome; he calls back to Sybil, in a vengeful tone, "I'm going to see Mr. O'Reilly, dear." Presumably, he is about to make good on his threat to insert said gnome into the builder. "...Then I think I might go to Canada," he adds, under his breath.
David Stubbs has rated The Builders as the weakest Fawlty Towers episode due to its reliance on stereotypes such as the battleaxe wife (indeed, this is the only episode to depict Sybil as a physically abusive and domineering wife), the feckless Irish labourer and the dimwitted Spaniard.
John Cleese himself named "The Builders" as "the least good" of the Fawlty Towers episodes that were filmed, owing to a general lack of laughter in the studio on recording day. He recalls that members of the Icelandic Broadcasting Corporation were visiting the studio that day and many of them were in the front row seats, apparently not entirely amused.