So you must sum up theme and conflict in one sentence, and it has to be compelling, interesting, and fresh. And if you work on them too long or look at them too many times you'll go frikkin crazy.
Here are some of mine, short story and novel alike,mostly in the "light fantasy or science fiction" category:
An uprooted man joins a theater to recover from a recent loss, and must delve impossibly far into the world of his character to save the lives of the cast.
Two young people fight for their own definition of true love, despite the decidedly strange physics which stands in their way. (That one is shooting for the odd genre of science fiction humor)
A away from home to rebel against .