MMMMMMMMM Delicious!!!

Just picked these from our Mystery Tree (Plum or Damson?) Quick wash and try, they are really good, sweet enough for me, but firm and just right. What are they? we don't know, but hopefully we will get a better crop next year, enough for tarts and jam etc. There are still twice as many on the tree, so we can have a couple of treats after our dinner.......