To get away from their hectic every-day life, they decide to go on a vacation. Withnail convinces his flamboyant Uncle Monty (Richard Griffiths) to let them borrow his cottage in the countryside by hinting that his best friend is a homosexual. Marwood does not know the particulars of the arrangement, but he agrees to go in order to get some relaxation.
Their trip does not go as expected. The cottage is cold and damp. It rains constantly, and they do not have any rain boots. They have to catch and cook their own food. They attempt to borrow food and supplies from some neighbors, but the neighbors are rude and unwelcoming. Withnail inadvertently offends one of them, and when an intruder enters the cottage, they believe he is coming to get revenge. It turns out, however, that Uncle Monty has decided to join them.
Uncle Monty seems like a blessing. He takes them into town where he treats them to fancy wine and a filling meal and buys them new rain boots. However, he has a few plans of his own on how to enjoy the holiday at Marwood and Withnail's expense.