The Ultimatum (Rystani #3) by Susan Kearney

Science Fiction Romance

What Goodreads says:

"Dr. Alara Calladar needs a man...
...but she sure as krek doesn't want one.

If Alara doesn't make love soon, her cells will fail to regenerate and she'll die. Unfortunately, her only option is an enemy--Rystani starpilot Xander, her abductor... and a member of the race who has been battling hers since the beginning of time.
Xander issues an ultimatum: He'll make love to Alara only if she will use her psi-talent of identifying DNA to help him find the cure for the deadly Terran virus spreading across the galaxy.
Alara is trapped. She gives Xander what he wants--and gets when she needs. But Alara holds a pair of secrets: the more they make love, the more Alara's cells adapt to Xander's body, until the only person she can make love with is him--and the more time they spend together, the more Alara likes Xander.
When it seems that all the forces in the universe have aligned against them, can Alara trust Xander with her life... and her heart?

The Ultimatium is book three in the Rystani series but it works very well as a stand alone.  Some of the characters from the previous two books are mentioned but are not really a part of this story.

Backstory:  Everything is presented as part of the current story and explains the tension between the characters and the reason for the mission the characters undertake.  While this is part of a series there was never a time when I felt that I did not have the background I needed to understand the world.

Characters:  Susan Kearney knows how to create interesting and unusual main female characters.  Alara’s is unique because during certain times she has to have sex to regenerate or she dies.  At times that overshadows how intelligent she is.  Xander is the alpha male who brings her on his ship without knowing about the need Endekian women have.  Both are strong intelligent people who have to work out their problems in order to sued in their quest.  There are some very well developed secondary characters who add interest to the story.  Then there are the Perceptive Ones who show up in small segments scattered between the chapters.  

Plot:   It is fairly standard.  There is a virus that will kill everyone unless a cure is found.  There is a time limit that adds to the tension.  Secondary is the attraction between Alara and Xandar.

Writing:  The writing moves the characters and the plot along in an interesting manner.  The dialog was crisp, the action fit the plot and the characters moved in the manner that fit their development.  A very well done book.

I liked the story.  I am looking forward to reading next book in the series, The Quest.  If you like SFR this is a good choice for you.

Bell Bridge Books published The Ultimatum by Susan Kearney in 2013. 

This is a reprint as Tor published this in 2006.

I received an ARC of The Ultimatum from Netgalley