Firebird by Jack McDevitt

Alex Benedict and Chase Kolpath are back in another adventure, with a challenging mystery at its heart. The sister of the widow of a somewhat famous physicist, Chris Robin, shows up with a trove of Robin's possessions that she wishes Benedict to market for her. As Alex is well aware of the value of "buzz" in generating handsome returns for artifacts, antiques and memorabilia, he sets out to find out as much as he can about Robin's disappearance, and arranges to be interviewed in the media about the man's odd disappearance.

Robin had been investigating ghost ship sightings and starship disappearances for some time before he, himself, went missing. In fact, the night of his disappearance, he and his pilot friend, Cermak, had just returned from space, where they had been performing the fourth in a series of experiments with dilapidated space yachts, trying to recreate the conditions whereby the craft would disappear from normal space time and re-appear periodically.

An interesting side plot develops after Chase and Alex visit the planet of Villanueva, which was the site of a horrible disaster thousands of years before when the planet entered a dust cloud and most of its population perished, leaving behind only its AIs to run things. Some of the AIs have gone insane and are hostile to human beings now, attacking anyone who lands on the planet. But the duo discover an AI, who calls himself Charlie, that is not hostile - he only wants to escape his millenial prison - and spirit him away with them.

Charlie tells them that there are other AIs, or Betas, still left on the planet that are also not insanely hostile, and enlists them in his crusade, quickly conceived, to recruit humans to rescue the Betas from Villanueva. Alex takes this show on the road, too, and there's some interesting philosophical and societal debate about what makes a being "human", possessing a "soul" and deserving of rescue.

The rescue theme continues through the end of the book when Alex figures out what happened when Chris Robin disappeared, and mounts a mission to find his ship, the Firebird, when it enters our universe for a brief sojourn. McDevitt poses some good questions about what a life is really worth, in terms of financial, societal, and political costs. I'm really enjoying these little scifi-cloaked mysteries.