I have a 7 year old Plum Jefferson. It had leaves and blossoms. Over night it has lost all. The tree looks dead, but if you break a branch, it is alive. The other plums trees are all ok.
This is a strange effect considering the other trees are fine.
Could this tree received more water then it's neighboring trees?
Could a drift of herbicide affected your tree?
Do you see any signs of damage, disease, or insects on the leaves or trunk?
Was weather cold prior to this event?
You will need to start by eliminating the possible cause.