Plum Tree dying?

I planted a Victoria Plum Tree in the ground two years ago. Last year it appeared healthy, and we had quite a few plums from it (I was surprised to get fruit in the first season). This year all started well, with decent blossom and small fruits starting to show. However, the tree now looks to me as if it is dying. The leaves have turned brown, and are falling off, whilst all of the fruit has shrivelled, becoming hard and under-developed. Some of the fruit has turned blue. I have watered the tree during the hot weather. Has anyone any ideas of what may be the problem, and what I can do about it?