There were always going to be casualties and my beginner's luck eventually ran out. In this case, a lovely purple streak from top to bottom, of what I assume is unfixed dye, ruining this set of negatives. With some Photoshop trickery, a few of the images might be workable but otherwise this roll will be consigned to the 'try not to do that again' history books. Up until now I'd developed 8 rolls of film without any major problems. There isn't much which can go wrong but little unforeseen things like this will probably happen more than once.