As a consequence of one of them ascending the Daa'Vit throne, several members of Captain Picard's former crew aboard the Stargazer are on the Enterprise and traveling to the coronation. The Daa' Vit and Klingon Empires had been at war for some time before the interjection of the Federation caused a cessation of hostilities. Despite the years of peace, the hostility remains and it is very difficult for the Klingon Worf and the Daa' Vit Morgen to occupy the same room. All of their instincts are to fight to the death, yet Morgen is a Captain in Starfleet and a close friend of Picard so both of them must bury their instincts and learn to tolerate each other.
That tolerance must quickly be turned into a working relationship, as there is an assassin on board the Enterprise that is determine to kill Morgen. The assassin is extremely competent in the technical sense, able to reprogram a holodeck into a killing machine as well as reprogramming food synthesizers and also extremely skilled in hand-to-hand combat. The situation is made even worse by the Enterprise inadvertently entering a subspace slipstream that moves them along at warp 9.5 and seems impenetrable. A secondary subplot is the effort that Dr. Crusher must make to keep her dead husband from her thoughts, for Jack Crusher served on the Stargazer and was killed rescuing the ship.
The action is fast, furious and consistent with the usual actions of the Next Generation crew. All perform admirably, Worf is the gruff Klingon that puts duty over personal feelings, Geordi is a miracle worker in engineering and Riker manages to woo and bed a female. Picard's former shipmates prove to be quite talkative to the point of insubordination yet in general they are all appealing, their conversations are much more open and honest, something that the Enterprise crew cannot do given their positions. Of course, the Enterprise is saved, the assassin discovered and disarmed and Morgen ascends the throne and galactic peace is preserved.
Some of the best stories are those where you know the literary destination beforehand yet the path there is so engaging that the foreknowledge is rendered irrelevant. This is one such story.