Full story
The movie starts mid-action, with Deadpool attacking a convoy on a highway, hunting a man named Ajax. He freezes everything, talks to the camera and rewinds to explain how he got there.
Wade Wilson was an ex-special forces soldier who made a living scaring bad people for cash. At his friend Weasel's bar, he meets Vanessa, just as unfiltered as he is, and they fall in love. A year later, he proposes. Soon after, he learns he has terminal cancer. A mysterious recruiter offers a treatment that would cure him and give him powers. To spare Vanessa from watching him die, Wade slips out in the middle of the night and signs up.
The lab is a torture chamber run by Ajax, a mutant who can't feel pain, and his partner, Angel Dust. The serum is meant to trigger mutant genes, and extreme stress is the switch. Wade learns that Ajax's real name is Francis and won't stop mocking him. As punishment, he is locked in a chamber that nearly suffocates him all weekend. It works: he gets a healing factor that wipes out the cancer, but his skin is left badly scarred. Ajax reveals the cured patients are sold as slaves. Wade breaks free, the lab burns and Ajax leaves him for dead, but he survives.
Ashamed of his looks, Wade doesn't go back to Vanessa. He puts on a red suit, takes a name from the betting pool at Weasel's bar and moves in with Al, an elderly blind woman. He spends a year killing Ajax's men to find him and force him to fix his face. That leads to the highway attack. Colossus and young Negasonic Teenage Warhead show up to bring Wade into the X-Men, and Ajax escapes. He finds out about Vanessa and kidnaps her.
Wade talks Colossus and Negasonic into helping and heads to a scrapyard where Ajax waits by a decommissioned helicarrier. Colossus fights Angel Dust, Negasonic accidentally brings the structure down and Wade saves Vanessa in the middle of the collapse. Ajax admits there is no cure for Wade's looks. Colossus asks him to spare the villain, but Wade kills Ajax anyway. Vanessa is angry he left her, but she sees his face, hears why he did it and takes him back. After the credits, Wade announces that the next movie will have Cable.