The whole film is seen through the eyes of Oscar (Nathaniel Brown), a guy who's living in Japan with his sister Linda (Paz de la Huerta) and who (in spite of his protests to the contrary) is a drug dealer and a drug addict. When he's tripping on DMT his friend Alex (Cyril Roy) comes to visit him and ask him about The Tibetan Book of the Dead he's lent him, which Oscar hasn't yet finished but is enjoying. But at the present time he has to meet Victor (Olly Alexander) to sell him some drugs, and he's waiting for Alex at a bar called The Void.
Alex walks towards the bar with Oscar, on the way telling him about his experience with datura. But he doesn't like the bar and waits outside while Oscar goes in. Inside, all Victor can say is he's sorry, and suddenly the police appear, Oscar dives into a toilet cubicle but it refuses to flush the drugs and the cops are hammering on the door. Still stoned, Oscar yells he has a gun and will use it, which causes the cops to shoot through the door and he collapses dead in a heap. And that's where Oscar's real trip begins.
What we have from then on is an out-of-body experience as Oscar sees what happens after his death, his spirit going over the past events of his life, and Oscar is even able to penetrate other people's minds, read their dreams.
Oscar's parents died in a car crash when he and his sister were young, and although they were sent to different children's homes they were very close and vowed never to separate. While living in Japan Oscar has managed, through selling drugs and through selling his body to Victor's mother, to pay for Linda's flight to join him, and she finds a job in a strip club.
After Oscar's death his dealer Bruno (Ed Spear), in fear of Japan's draconian drug laws, gets rid of his drugs and Alex takes to living on the streets. Linda is in a relationship with her boss Mario (Masato Tanno), gets pregnant and has an abortion. Oscar experiences his mother breast-feeding him, sees Linda and Alex going to a love hotel, sees inside his sister's vagina, sees sperm uniting with ovum, and via a process of false memory experiences his own birth.
Enter the Void isn't a difficult film to understand once the pieces of the jigsaw are put together, although it's quite a mind-blowing visual experience.