At a car boot sale, Ryan comes across a mobile phone being sold for £20. He suspects it is stolen, but the salesman persuades him to try it. Ryan sees the model number "DIAVOLO 666". At home he finds that the phone had a channel called Diavolo Special that shows violent and pornographic films.
That night the phone's screen flashes an image of a figure that looks like a man and a goat. Ryan has the feeling that something is in his bedroom. Then his nightmares begin. The phone appears to read Ryan's mind, switching to a channel reflecting his thoughts. The phone continues to exhibit strange behavior on subsequent nights, showing strange numbers and the word "PAYBACK".
One day in the street, Ryan sees a flying creature which he has seen on the phone. He sees it prey on two starlings, but no one else notices.
One morning the phone rings, and when Ryan answers, the words "The time is nearly up" come in a menacing whisper. Ryan fears that he is going to die. but does not want to give up the phone. The phone rings and plays the same message again.
On Halloween, one of Ryan's friends points out that the phone appears to display the time an hour ahead. Ryan thinks this means the payback is to take place at 23:55 that evening.
He leaves to get home before the payback. A man confronts him with a knife and demands his money and phone. Ryan hands it over and tells him how to use it. The thief gets the same nosebleed Ryan had when he first got the phone.
As the thief leaves, the phone gives out a high-pitched whine, and the flying creature goes towards him. The thief tries to escape but the creature pushes him onto the main road, where he is hit by a car and run over by a van. At the crash site, Ryan finds the crushed remains of the phone melted into the tarmac.
