Dr. Alara Calladar is a biologist with a uniquely personal mission - to cure herself and all the women of Endeki, her home planet, of the Boktai. Boktai is a hormonal imbalance of sorts that causes women to mate or die. It occurs every other year in a woman's adult life. Alara has seen first-hand, through the complicated and difficult relationship between her beloved mother and cruel father, how Boktai can enslave a woman to her own passions. She has made it her life's work to free women from the bondage that their sex places on them.
Of course, this hasn't left the lovely, golden-skinned, pink-haired and green-eyed Dr. Calladar with much time to find love in her life. Enter Xander, a Rystani starpilot and captain of the Verazen. He has come to ask her to help him and his crew find a cure for a virus that threatens the lives of billions.
Dr. Calladar can't leave Endeki - and doesn't want to. She has no desire to help a Rystani. The Rystani killed her parents in an act of terrorism. Her only sibling died in the Endekian-Rystani war. Xander, a fantastic male specimen, doesn't care much for Alara's people. The Endekians killed his mother and took him hostage. They tortured him, too.
Xander is nothing if not persistent. Dr. Calladar's refusal doesn't stop him from getting her to come with him and his crew. He goes over her head, so to speak, and exchanges one of his crew members, Kirek, for Dr. Calladar. Kirek is left as a hostage and sexual plaything for the Endekian leader's daughter and her "friends."
Xander kidnaps Dr. Calladar, who is deep in Boktai and must mate to regenerate her cells. Xander offers - somewhat reluctantly - to help her. The two have frequent contact throughout their dangerous mission to find the "Perceptive Ones," the creators of the universe who have left pure DNA which, if found, can be used to manufacture a cure for the virus killing Terran, Endekian, Rystani and more. In time, Dr. Calladar and Xander fall in love. They learn to put aside their differences and save the world in the process...with a little help from their friends and a mysterious stranger named Clarie.
All in all, The Ultimatum is chockful of action, romance and sex. Kearney's prose will make you sweat. The world that she creates is full of plot twists, turns and thrills. Just suspend your disbelief and enjoy the ride.