Thanks to prompt action on Janet's part, the bootable USB stick was in the post box when Roar and I went up to the post office this afternoon. Ten minutes later, I am relieved to find everything looking much the same as it did before the file system got corrupted.
I'm hiding in the outbuilding that Roar calls "The Library" at the moment. Now I should probably put the laptop away. If he finds I've smuggled one into his island paradise, he'll probably slip it quietly into the sea while my back is turned, and that would be more difficult to recover from!