Star Trek The Next Generation, book 46 : To Storm Heaven
Esther Friesner1997

When Lelys, ambassador of the plague-ridden colony planet of Orakisa, approaches the Federation seeking help for her dying world, the USS Enterprise speeds to the rescue. Captain Picard and his crew escort the Orakisan delegation to its long-lost sister world, Ne'elat, where the ambassador and the away team are initially welcomed, but then endangered. As the Enterprise officers make their way through a web of planet-wide intrigue, time is running out for the people of Orakisa and the inhabitants of all their sister-worlds as well.