Starbound, by Joe Haldeman

The first book in this latest series by Haldeman, Marsbound, was a pretty good read, very much an homage to Heinlein's Podkayne of Mars, in my opinion. The heroine, Carmen, was the first human to make contact with the "Martians", who are actually beings designed by The Others, vastly powerful entities from insterstellar space. They have been observing humans on Earth for thousands of years, and apparently decide that they are too dangerous to be allowed to survive, so they attempt to destroy Earth at the end of the novel. Obviously, their plans are thwarted, otherwise we'd have no sequel in Starbound.
The governments of Earth, Luna and Mars have decided to send an expedition to contact The Others, to try to plead with or reason them out of their decision to destroy Earth. Carmen, and her husband, Paul, are two of the members of this mission, which will take seven years, subjective time, but much longer from an Earth reference frame, due to relativity effects.
Most of the novel is the story of their voyage, which is mildly amusing. There are four humans from Mars, three from Earth, and three of the "Martians" on board the voyage. Their interactions and discussions of alien philosophy go on for about three and a half years, to the "turnover" point when the ship must begin deceleration. At that point, I think even Haldeman got tired of their issues, and decided to cut things short. When they enter free fall at turnaround, they are met by a representative of the others, a biological construct, who tells them they are to be allowed to meet The Others, instead of being destroyed out of hand. He makes use of a very convenient (to us and the author) way to travel without experiencing subjective time, all the way to the home planet of The Others, and then back to Earth. Thanks, Joe, for saving us from another ten years of Peyton Place in Space.
On their arrival at Earth, they deliver the aliens message, but once again Mr. Haldeman takes a short cut, leaving us with a very unsatisfactory ending. If there turns out to be a third in this series, I'd be really surprised.