Precurser,Defender,Explorer, by C.J. Cherryh.
More in the 'Foreigner' universe! A second trilogy -- not stand-alone, per se. Over the course of the first trilogy, the starship Phoenix returns to the atevi homeworld, where atevi and a small human colony live uneasily. The second trilogy covers what happens when the ship crew finds out they might have been lied to by their captains, Phoenix goes on a new mission, and Bren Cameron does what he does best -- connect with a new species.
