Fire on High (Star Trek New Frontier, No 6)

Lieutenant Robin Lefler's mother died in a shuttle explosion ten years ago. So is the woman being held prisoner in Thallonian space really her? If it is, what is her connection to the mysterious woman holding a weapon that could doom entire worlds? With the lives of billions at stake, Robin Lefler, Captain Calhoun and the crew of the U.S.S. Excalibur must find the answers before time runs out for them and for the struggling remnants of the once-great Thallonian Empire.