The mystery of the Chindi itself — the artifact our heroes are concerned with, its origins, its nature — is at the heart of the story. McDevitt handles it so well. Rather than dumping exposition, he lets our heroes circle around it, finding new angles, new contradictions. Each discovery feels earned. The mythology he constructs around this thing is unsettling, and the implications only go deeper as we progress. It's the kind of SF mystery that makes you want to immediately reread it to catch what you missed.
My one tiny gripe is that we have yet another last-second rescue under catastrophic circumstances. Our heroes pull off the impossible for the 3rd time in a row. It's a minor flaw in an otherwise excellent series, but the pattern is there. Is it a big deal? No. Is the book any less good because of it? No.
Great read!