Men will do anything to live forever...
There are those among us that are different, who have the gift of Immortality. But they must hide in plain sight, in order to live full productive lives. Or as full as their 'gift' will let them. They can love and be loved, but very few, if any, are given the real gift of life and are able to reproduce.
But there are those that want to live forever and pass it on to their own. They've been trying for years, hidden well within the government, and testing on unwilling or unscrupulous humans.
And after numerous tries, have finally been able to create a hybrid.
Soon, they will have the power they so desire.....