Update: this converter is now built into Twine 1.4 (in the "Import Compiled HTML file" menu item), so this page is no longer necessary.
Someone on my Twitter feed reported that they'd lost the source code of a Twine game of theirs, and wanted to know if they could convert the HTML back to a usable format. So, I decided to quickly knock up a utility that could do that. Here it is - it extracts the passages from a HTML twine game and converts them to Twee source code, which Twine can import using the "Import Source Code" menu option. I hope it works for you.