James Frey, a 23-year-old man who has spent the majority of his life abusing drugs and alcohol, wakes up on an airplane with no idea how he got there or where he's going (the island from Lost, perhaps?). His parents (who somehow knew where to pick him up) grab him at the airport and take him to a rehab Clinic in Minnesota.
This isn't the fun kind of rehab with movie stars hanging out everywhere: James has to go through painful oral surgery without anesthesia, deal with horrible withdrawal-induced hallucinations, and learn to cope with his own anger-management issues.
Along the way, James meets Lilly, a female patient at the clinic; Leonard, a mob boss who takes James under his wing; and a variety of counselors, psychologists, roommates, and other patients who run the whole spectrum of helpful to hurtful and who represent every form of drug and alcohol abuse under the sun.
When James is told that he will die if he does drugs again, he decides, well, that's an easy way to kill himself, so he plans to leave the clinic and go out in a blaze of glory—glory being the street name of some obscure drug Frey has probably snorted. Leonard convinces James to wait 24 hours before ending his life, and during that time, James's brother visits, and his relationship with Lilly begins to grow.
James eschews the Twelve-Step program in favor of the Tao Te Ching, a book of Chinese philosophical poetry given to him by his Brother. He takes Leonard's philosophy—of just "holding on," like Carnie Wilson—to heart. He falls in love with Lilly on their forbidden walks through the forbidden woods. They plan to move in together in Chicago after getting out of rehab... and after James serves his three-month jail sentence.
Eventually, James stops puking every day and makes amends with his parents who come to visit as part of the clinic's Family Session. Unfortunately, right around this time, he and Lilly are caught together and banned from seeing each other again. Lilly takes to this rule about as well as James takes to any rules, and she rebels by running away from the clinic.
James rushes after her, finds her inside a crack house, and brings her back to the clinic to recover. Everyone at the clinic is so impressed that he didn't smoke an avalanche of crack while he was out that they agree to let him leave the clinic. Leonard leaves around this time and decides to make James an honorary son. James makes an inventory of all the wrongs he did (22 pages of wrongs, to be exact) and makes a confession to a priest.
When his brother picks him up, James demands to be taken to a bar so he can order a giant glass of whiskey and not drink it to prove just how rehabbed he is. In the epilogue, we learn that James has never relapsed, but both Leonard and Lilly have died since leaving the clinic.