a modern Faust

Will and his cousin Tim are in the attic on the day before New Year's Eve, looking for an old book of their grandmothers. As Tim finds the book, Will finds a different book - an ancient book, handwritten in Latin hundreds of years ago. He reads it out for a laugh, over the Christian Tim's protests. A demon appears in the attic, billowing smoke everywhere, and the two boys run, terrified. The demon is visibly disappointed by this waste of his time, but suggests that he has an idea to claim Will's soul.
The boys are shaken but unharmed, and they talk through the night. They realise that this proves the existence of God, something which Tim finds inevitable and Will terrifying. They resolve to be good people, and Will promises Tim that when Tim has left for home (in Wales) he will burn the book.
Will means to burn the book, but cannot bring himself to do it. He considers selling it, but does not want anyone else to cast the spell. He puts it back where he found it, too afraid to do anything. He starts going to church, a shocking turn of events for his parents. He questions the vicar ferociously, determined to find out exactly how he should be behaving.
He joins a local Christian youth group where he meets Emily, a girl he grows very fond of. He is doing well and being a good Christian, but finds some passages in the Bible that disturb him. He has a serious conflict of faith, and begins to research other denominations of Christianity. He walks home from school after a heating argument with his friends who think he is becoming boring, and wonders how he never saw God before, with all the beauty in the world.
Emily gets cancer, and Will at first refuses to believe it. He visits her in hospital every day, bringing flowers, sweets, books and a card from the youth group. He prays for her to live. She gets weaker and weaker, and doctors are pessimistic.
Weeks pass, and Emily is close to death. Will makes all sorts of promises to God - he swears to be good, and give to charity, and volunteer, and become a human rights activist, or a monk, all sorts of things. When Emily's parents tell him that she has lost consciousness and is likely to die soon, he goes home and breaks down completely. He is distraught, and furiously angry with the cruelty of God.
Will decides that, whatever his own beliefs, his utmost concern is for Emily. He summons the demon again. The demon suggests that he come back later, as necromancy is wonderfully evil. The demon says that Will can have 24 months of all the powers of hell, in exchange for his soul. He reluctantly accepts.
The demon then tells Will that he can only do evil things. Will is shocked and furious. The demon mocks him, and Will tells the demon to kill himself. The demon says that he wishes he has that power. Will tells the demon to return to hell, and the demon says that he brings hell with him.
Will realises there must be a loophole. He tells the demon that Emily's mother had accepted her death as the will of God, and that curing her would therefore thwart God's plan. The demon replies that, for all they know, everything is God's plan. The demons themselves do not know if they are not just some tool in the divine plan: they disagree with God whatever he says: they do not know what he wants them to do, but they suspect that they always do it. Will is fascinated, but determined to find a way to save Emily.
The demon is impressed, and says that Will reminds him of someone he used to know. He says that love for one person, selfish love, is a great product of hell. He suggests that 'Thou shalt not kill' could be seen as applying for individual cells, and that he could therefore go and kill a part of Emily. Will, ecstatic, commands it at once, and thanks the demon.
The demon comes to Emily in a dream, and tells her what has happened. She is surprised to be addressed, and horrified at what Will has done. When she wakes up she tries to avoid him, which confuses her parents.
Will comes to see Emily, thrilled that she is alright. She is less enthusiastic, but realises that he does not intend to tell her the truth. She accepts this, and decides to stay close to him, in the hope that she can save him.
The demon argues with Satan, telling him that the cancer was not part of the plan: Will was supposed to fall for selfish reasons. Satan tells him that Will is being selfish - and that God is the one who is cruel for allowing him to do this.
Will does good things through loopholes, working together with the demon - 'Make him discover the cure for AIDS, so we can all have UNPROTECTED SEX!', 'If he's busy solving world poverty, he will NEGLECT HIS FAMILY!' etc.
The end of the time approaches. Will comes to Emily, determined to come clean and tell her the truth, just as their relationship has become sexual. She reveals that she always knew, and she is sure that if he repents, he can still be saved. Will does not believe that this could happen.
Will continues with his work, but cracks appear. The world is as complacent as the Gotham City Police Department, and there are no easy solutions.
The demon tells Emily that Will cannot repent, because she is alive. She tells him that she loves him, and then kills herself.
Thinking Emily is still alive, Will asks to speak to various people. The demon can summon illusions, but can only summon the real person if they are in hell. Will speaks to several notorious figures. The demon is revealed to be taking the form of Judas when Jesus arrives, invited but not summoned. Jesus and Will argue, and Jesus essentially storms off.
Will says that he would go to hell before supporting God. The demon reveals to Will that Emily is in hell. She is summoned and they talk. She convinces him that God is good and kind, but that she made a mistake in thinking that killing herself was a solution. She urges him to save himself, while he can, like Lazarus. Will repents, and weeps, sobs, and prays God to deliver Emily from hell, having realised that dying of cancer would have sent her to heaven.
Will is instantly returned to when he summoned the demon deliberately for the first time. The demon suggests that he come back later, as necromancy is wonderfully evil. The demon says that Will can have 24 months of all the powers of hell, in exchange for his soul. Will asks for a few days to think about it, which the demon grants.
Whilst thinking in church, Will has a vision of the events which have happened. He thinks it is a warning, and decides not to summon the demon after all. He thinks it is worth the risk of him going to hell, but not for Emily. Emily gets better, and they live good Christian lives. Secretly, Will considers this his failure.