A lot of the plums were beginning to show patches of redness amongst the green, so I picked up 16 lbs of those and soaked them overnight in metabisulphite solution - that was to kill off anything I didn't want, but it seems to have softened the fruit a little as well. At the moment, they are sitting in a syrup of 2kg of sugar and a couple of gallons of boiling water. When that's cooled later, I'll chuck in some yeast and nutrient and, after a couple of days, get my hands in there to squeeze the fruit and extract the stones.
According to what I can find on the web, there's not a great deal of chemical difference between an unripe plum and a ripe one apart from sugar and water content (and a bit of tannin and colouring in the skins). WARNING - EXTREME OPTIMISM AHEAD If that's so, then this stuff should turn out just like any other plum wine as long as I adjust the added sugar correctly END OF OPTIMISTIC FORECAST.
So, right now I'm debating with myself whether or not to add some apple juice and orange juice, both to improve the acidity balance (the plums are surprisingly unsour - not exactly yum yum edible, but not as bad as I thought) and to add a "fruity character" which the plums may not have developed yet. I think I'll almost certainly add some raisins/sultanas (depending upon what I can find in the recesses of the cupboards).
If this works, I have some great ideas for those unripe windfall apples and pears

Mike