Plot

NOTE: In the published screenplay, "I" is called Marwood but the character is unnamed throughout the actual film and on the end credits.

Camden Town, London, September 1969. Marwood (Paul McGann) and Withnail (Richard E. Grant) are unemployed actors who share a squalid flat and their only visitor is their drug dealer Danny (Ralph Brown). Sick of his surroundings, Marwood desperately wants to get away for a break and suggests to Withnail that he asks his Uncle Monty (Richard Griffiths) if they can spend a few days at his country cottage.

Monty is an eccentric gay man who is getting on in life, and who Withnail frequently lies to about how well he is doing as an actor. Upon visiting him at his home in Chelsea, Withnail and Marwood share some wine and a conversation with him before Withnail talks to him alone in the kitchen. When Withnail and Marwood leave, Withnail reveals the keys to the cottage.

When the pair arrive at the countryside, they find themselves completely out of their depth. They burn some of Monty's furniture to keep themselves warm, and struggle with the idea of killing and plucking a chicken.

At the local pub, where the bartender gets as drunk as they do, they encounter the local poacher, Jake,(Michael Elphick) who has some pheasants for the barman and some eels for himself, which Withnail and Marwood want but he refuses. He takes Withnail's cigarette and Marwood gives him his pack, and then tells them he might bring them a rabbit sometime. Despite this, he continues to belittle them and says they want working on.

The next day, sick of eating vegetables, Withnail goes fishing with a shotgun. On the way back, they see Jake walking away from the cottage. Anxious and scared, Withnail wants to share a bed with Marwood while keeping the shotgun in his hand. Marwood tries to take it and Withnail accidentally pulls the trigger, putting an hole in the ceiling. Covered in plaster, Marwood angrily throws the gun out of the window and takes Withnail's room. A little later, Withnail comes in and once again gets into bed with Marwood telling him he can hear noises. The noises get and louder and louder, and as they both clearly hear footsteps coming upstairs and approaching the door, they fear for their lives. The door opens but it's not Jake, it's Monty who has come to join them for a break.

The next morning, feeling uncomfortable around Monty's obvious attraction to him, Marwood tells him that he and Withnail have to get back to London to sign on for their unemployment benefits but Monty isn't having any of it. He tells him he's come along way to see them and wants to spends some time with them. He gives them some money for some Wellington boots so they can go hiking, but Withnail instead tells Marwood that they should go to the pub. After getting drunk, the pair head to a cafe for something to eat in order to try and soak up some of the booze before Monty picks them up. They enter and help themselves to some food without paying while pretending to be eccentric millionaires.

Over dinner, Marwood sees that Withnail isn't in a rush to go home after all. He confronts him away from his uncle and Withnail tells him he couldn't let the old man down after coming a long way. But Marwood's feeling increasingly uncomfortable and anxious around Monty. While the three of them enjoy a walk together, Marwood makes it clear to Withnail. He wants to sleep in Withnail's bedroom because that has a lock on the door, Monty takes his room, and Withnail sleeps in the living room. Withnail agrees. For a brief moment, Marwood is relieved and doesn't think there's any need for sleeping arrangements after all when they spot Jake once again in the distance hanging around the cottage. Marwood tells Withnail the holiday's over and it's time to go home. But when they get to the door, they discover Jake wasn't looking for trouble and has instead left them a rabbit for dinner.

As the night draws in, Withnail, Marwood, and Monty have a drink and play cards. Withnail ends up drunk again, and Monty says he should go to bed. Marwood tells him that Withnail's sleeping downstairs but Withnail says that he wants a bed. Marwood hastily helps Withnail up to bed, wishing Monty goodnight. He puts Withnail to bed with the intention of joining him after getting a blanket from his room for himself but he sees Monty outside the door who has locked Withnail in. He says he should sleep alone to sleep off the booze. Marwood suggests he take his room and he'll sleep on the couch. Monty becomes increasingly forward with Marwood and starts asking him if he's ever tried different experiences, and seems upset that Marwood is avoiding him. Marwood says there's nothing wrong other than him being very tired. Monty tells him to go to bed and he'll take the couch.

Marwood is laying in bed in panic mode, with his eyes fully open, and a chair pushed up against the door. The door is kicked open, and Monty enters in his dressing gown, wearing make-up. Marwood tries to pretend to be asleep but Monty is persistent and is determined to talk to him. Monty tells him he tried his best not to act on his feelings and that he tried his best to stay away but he couldn't help himself. Marwood is shocked when he reveals that Withnail has told him that he's gay and that he knows he' had sex with men in public toilets. Monty tells Marwood not to be ashamed of his sexuality anymore. Shocked, Marwood tries to get out of the bedroom but ends up in a corner with Monty approaching him and revealing his naked body underneath his gown. Marwood panics and while fending Monty off, tells him that Withnail has lied, and that they're actually both gay and have been lovers for six years but Withnail is unable to admit the truth about his homosexuality. Monty is distraught and feels ashamed of himself.

Marwood confronts Withnail who tells him that lying was the only way to get the cottage and that he never actually expected Monty to make the long journey to join them. Monty leaves a note for the two of them, wishing them happiness together. Just as Marwood finishes reading it, feeling sympathetic about the old man, a telegram arrives for him. It's for an acting job that might be his, and he wants to leave immediately.

While Marwood sleeps in the back of the car, Withnail, drunk on a bottle of wine he's had with his dinner, speeds along the motorway, and is stopped by the police and arrested.

When they finally arrive home, they discover Danny has been sleeping in Marwood's bed, and he also has a friend in the bath. While they share a big joint, Marwood reveals that he hasn't got the acting job he was after but instead the lead role. Withnail congratulates him with a smile but he knows full well what it means for their friendship as the job is in Manchester.

Marwood packs a bag and tells Withnail his dad will pick up the rest of his stuff later in the week. Withnail recommends they have a final drink together in the flat and have a glass of wine but Marwood tells him he has to get going. Withnail suggests they share the bottle while walking to the train station together. As they walk through Regent's park in the pouring rain, Marwood tells him he doesn't want him to walk any further with him. They both reveal they'll miss each other, and Marwood goes off to start his new life. Withnail, umbrella in one hand, and bottle of wine in the other that he takes an occasional swig from, performs Hamlet's "what a piece of work is a man!", with no audience, other than a few wolves in a zoo enclosure. Soaking wet and emotional, he takes a bow and walks off alone.