Star Treks with DD!
[Just catching up - I've read the Wounded Sky multiple times - some ways the most "Narnian" of Duane's Trek books (think "The Voyage of the Dawn Treader"), and - at last I read The Empty Chair. Romulans done right!]
Wounded Sky (Star Trek TOS #13) by Diane Duane
An alien scientist invents the Intergalactic Inversion Drive, an engine system that transcends warp drive -- and the U.S.S Enterprise will be the first to test it! The Klingons attempt to thwart the test, but a greater danger looms when strange symptoms surface among the crew -- and time becomes meaningless.
Now Captain Kirk and his friends face their greatest challenge -- to repair the fabric of the Universe before time is lost forever!
The Empty Chair (Star Trek: Rihannsu, Book 5)
by Diane Duane
THE CULMINATION OF A SAGA
TWENTY-TWO YEARS IN THE MAKING.
They call themselves Rihannsu -- the Declared. To the Federation, they are the Romulans. By any name they are adversaries as formidable as they are inscrutable. Self-exiled from Vulcan in ages past, they retain an ancient martial philosophy and a code of conduct that has sustained them through centuries of hardship, warfare, and thwarted ambition.
Now their empire is gearing for war once again. Armed with the revolutionary Sunseed technology, which can destabilize entire stars, a Romulan vessel is warping toward the heart of the Federation. Its target: Earth's sun.
But this offensive comes at a perilous time, as a growing number of Romulan worlds are joining a revolution -- one led by the renegade Commander Ael t'Rllaillieu of the warbird Bloodwing, with the aid of Captain James T. Kirk of the Starship Enterprise™ and the Hamalki physicist K's't'lk, the Federation's foremost authority on Sunseed technology. As the threat to Earth looms ever larger, Bloodwing and Enterprise lead an armada toward the Romulan homeworld for a final reckoning that will decide the future of the Rihannsu people.