Death at a Funeral

The story is set in England and takes place mainly at a family home where Daniel and his wife Jane live with his parents. When the story opens, it is the day of Daniel's father's funeral and, while in the process of organising this event, Daniel and Jane plan to purchase a flat and move away from the parental home. Daniel's brother Robert, a renowned novelist living in New York City, would rather spend his money on a First Class airline ticket to England than help finance the funeral, leaving Daniel to cover the burial expenses. As guests begin to arrive at the family home, where the funeral service is to be held, he struggles to complete a eulogy, although everyone expects Robert the writer will be the one to deliver some appropriate remarks.Daniel's cousin Martha and her fiancé Simon are desperate to make a good impression on Martha's uptight father Victor. Their hopes for doing so are dashed when Martha, hoping to calm Simon's nerves, gives him what she believes is Valium but actually is a designer hallucinogenic drug manufactured by her brother Troy, a pharmacy student. While on the way to the funeral, Simon begins to feel its effect.A dwarf named Peter introduces himself to Daniel, who is too busy to speak to him at that moment and suggests they talk later. None of Daniel's relatives can identify the man.The service begins and the hallucinating Simon, certain the coffn is moving, tips it over, causing the body to spill out onto the floor. During the ensuing chaos, Martha drags Simon outside, where her father forbids her to marry him. When Simon is told why he is reacting as he is, he panics and locks himself in the upstairs bathroom. Martha tries to persuade him to open the door while fending off the unwelcome advances of Justin, with whom she once had a one-night stand that she deeply regrets and would like to forget. When the drug overcomes Simon, he steps out of the window naked and sees Justin kissing Martha. Thinking what he sees reflects mutual feelings, he proceeds to climb onto the roof, where he threatens to jump. Hoping to calm him, Martha reveals she is pregnant with their child.While most of the guests are caught up in Simon's seeming insanity, Peter meets privately with Daniel and Robert and reveals he was their father's lover. Unhappy that he was left nothing in their father's will, Peter reveals photographs that prove his relationship, and attempts to blackmail the family for £15,000. The brothers panic and bind and gag Peter, and to calm him down they give him the hallucinogenic drug they also believe is Valium. Peter manages to free himself, but in his drug-induced state he jumps repeatedly on the sofa before falling and hitting his head on a glass coffee table. Troy and family friend Howard cannot feel a pulse, so they believe Peter to be dead. Forced to dispose of the body as quickly and surreptitiously as possible, Daniel and Robert decide to place it in the casket with their father.The service resumes, and Daniel's awkward eulogy is interrupted when the still very-much-alive Peter leaps from the coffin and the compromising photos fall out of his pocket for everyone, including the widow, to see. Daniel demands everyone stay calm and declares his father was a good man, although clearly one with secrets, and he delivers a loving tribute to the man.That same night after the all the mourners (including Peter) have left, Robert tells Daniel that he plans on taking their mother to New York so that Daniel and Jane can finally get an apartment and live alone like they'd always wanted. Their conversation is interrupted when Jane shows up and tells them that Uncle Alfie will be staying over that night because of his panic attack after having seen Daniel and Robert move the body. She also tells them that she gave him some "Valium" (unbeknownst to her it is actually Troy's hallucinogenic), which shocks Daniel and Robert. The scene cuts to a shot of Uncle Alfie on the roof, naked like Simon had been, complaining about how "everything is so fucking green".

Question: Where does Simon lock himself when he learns why he is reacting as he is?
Answer: In an upstairs bathroom.