These aliens have been away from Earth so long they no longer consider themselves human. They lost their women to a virus in space and returned with high hopes. In the few hundred years they've been back, they've run into problems.
Incapable of mating until they've 'Been Blued', they search for women who will show them the affection and commitment their symbionts require for the process to begin.
Resorting to a reconfiguration cloning technique has given them a reprieve from pending extinction, but their time is still running out.
The struggle to respect human free will seems to limit their possibilities; a few of them find the concept open to interpretation while others just want to return to space. One day a human accidentally Blues an alien. She has plans of her own, and they don't include being matriarch to a new species. If her prospective husband and his friends can't change her mind, they may not have a future.
To complicate matters, the symbiont has started to spread to mankind. Its slightly telepathic nature will make avoiding detection by the humans that much harder. What's a fun loving alien to do?