Your hero and his female counterpart are the world's saviors, but to activate their uber-nature they have to have sex.
Enough said.
But I'll go on; just before it abruptly ended they had less than ten minutes to find each other and do the deed before the men and women associated with the main hero would be wiped out by the infinitely powerful evil. (I so want to find out what happens...do they make it in time; er, uhm I mean do they save the day.)
The hottest genre: fast breeder fiction