Fifth in the Alex Benedict series.
Set in the relatively distant future -- at least two thousand years or so -- this series features Alex Benedict, an antique dealer. And when one is dealing with interstellar travel, antiques can be very old indeed.
In this case, the central artifact isn't all that old, but it's certainly intriguing. It's a stone tablet with inscriptions that aren't in any known human language, and it's found at the former home of an explorer who devoted his career to the search for non-human life. Only one alien species has ever been discovered, so Alex is quite excited at the possibility that this tablet could lead to a second.
There are mysteries, though. Sunset Tuttle, the explorer in question, was something of a publicity hound, and if he had found alien life, it seems unlikely that he would have kept it a secret. The tablet's current owner, who was once Sunset's lover, gets very nervous when Alex starts asking questions, and does all she can to keep him from getting a good look at the tablet.
Alex and his assistant, Chase Kolpath (who narrates the story; she's sort of a Dr. Watson to Alex's Sherlock Holmes), set out to unravel the secrets of the tablet, a quest that will interstellar sightseeing trips, retired spaceship pilots turned hermits, and a menacing woman known as the Mortician.
McDevitt's style isn't flashy; it's comfortably old-fashioned. His future is not a particularly high-tech place, and it feels much like our own might if we took space travel for granted. Alex and Chase aren't the deepest or most complicated characters, but they're likable, and it's pleasant to spend some time in their company. They mystery of the tablet is well plotted, and comes to a reasonable and believable solution. Echo doesn't break any new ground in the genre, but it's a solid story, well told, and sometimes that's more than enough.