Harry Potter and the One Ring of Plasticine
If Hermione Granger had not disobeyed Dumbledore's orders by an amazing twist of know-it-all casuistry, and had otherwise obeyed them strictly, and if Harry had not discovered that he was rather good at modelling with plasticine, a lump of which he discovered in Dudley's old toys in his bedroom, things might have gone differently.
The casuistry was for Hermione to send through the muggle post four books to Harry. One of them was a book of runes, 'in case you want to drop divination and do something more sensible now that you've seen what a waste of time your electives are'; and 'because you could do with some light reading' three handsome volumes of 'Lord of the Rings.'. There was a note which basically informed him that Professor Dumbledore had forbidden her to correspond with him. She gave her phone number, however, and explained that his parcel was not going to be tampered with because when she had jabbed his wounded arm in the train carriage, she had taken enough of his blood to write Dursley-repelling charms on the wrapping paper and reminded him that Dobby would love to feed him.
Harry was torn between outrage and thinking this quite brilliant; and not feeling like looking at runes, pasted the wrapping paper on his door.
It was magical. With Dobby feeding him, it was the quietest time ever in Privet Drive.
And then he was carried away by the tale of the Lord of the Rings, and the rings of power. And idleness breeds an at times warped imagination, and Harry found himself modelling a ring which was essentially morsmorde, whispering to it in parseltongue as he worked.
"And of what use is a plasticine ring," said Harry, in disgust. He did not destroy it, however; it was a small work of art. He sighed, and leafed through the rune book.
The chapter 'using runic arrays for transfiguration' caught his eye.
And he went back to read the book from the beginning, gasping as he realised that almost any spell effect could be duplicated by runes, even if it was not as fast.
It took a bit of practise to start getting runes to work for him; and those given in the book were too limited.
Harry decided to turn his hand to using Tolkein's runes.
Things went a lot better then.
Especially when Vernon, on the way home from an office party, blundered into a runic circle Harry set up and spent the rest of his natural life as Harry's toothbrush. Petunia naturally called the police when her husband failed to return. He had accepted a lift from a colleague, as he had been totally bladdered, but the colleague, who was also the worse for wear, only said that he had dropped him at the end of the road, not wanting to have anyone of the neighbours realise who it was who had totalled the parked BMW outside number 7.
Grown men are allowed to disappear, and nothing was really done about it.
Then Harry worked on turning plasticine into metals.
And when he had it down pat, the one ring of plasticine became a silver ring.
And Harry knew a few names of Deatheaters, from those who had been in the graveyard.
Petunia grew used to dreaming that she heard a thump, accompanied by a brief... a very brief... yell.
And Harry had a collection of Dungeons and Dragons figurines which were quite impressive. The deatheaters would land in his runic circle, and promptly transfigured.
And in the darkness of Dudley's cupboard he bound them.
Except Peter Pettigrew.
Peter Pettigrew was sent through the post to Amelia Bones, anonymously, explaining that this plastic rat was an animagus death eater.
Peter had never seen who had brought him and transfigured him; he had been attending the Dark Lord one minute, and the next he was in the presence of a disembodied hand with a ring which had commanded him.
He sang like a canary.
Sirius Black was soon being declared innocent.