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Cain is a career military woman who divorced her husband well before the Battle of Tauron, with whom she had two daughters, Helena and Lucy Cain. The divorce occurs as a result of her unwillingness to give up flying Vipers.
In the days following the end of the war, Cain is assigned to Galactica as CAG when the ship is ordered to hunt for a rogue Cylon cell called the Annihilators. During her tenure, she proceeds to push Adama and the pilots under her command to their limits, but earns their respect, particularly in Adama's case. She takes a special interest in Adama, as he becomes her right hand man and both become friends who often spar against one another through pyramid.
On a mission to hunt down the remaining Annihilators at Trinity Base, Galactica is boarded by Annihilators en route to that base, where the Cylons manage to decompress the ship and begin turning Galactica's weapons towards the battlestars accompanying her: Ulysses and Cerberus. A nuclear missile is fired before Cain, Adama, and a team of surviving crew members in EVA suits are able to remove the Annihilators from Aft Damage Control. However, in the process of securing it, Cain is stabbed through the chest by a Centurion, mortally wounding her.
As part of his promise, Adama delivers two letters that Cain had written to her only surviving child, Helena, and to Cain's own parents, who had apparently survived (Battlestar Galactica: Origins 5, Battlestar Galactica: Origins 6).