A couple of the recent episodes have had mysteries as strong as the character work, but this time, the mystery was pretty obvious. As soon as that one character mentioned in passing that Susan had been "vaporized" in the explosion, it was obvious that she'd survived and gone into hiding and was the real killer. Heck, in fiction, "vaporized in the explosion" is always code for "alive and in hiding," and that's one fictional trope that actually makes real-world sense. I'm fairly sure it's physically impossible for a human body to be totally vaporized in anything short of a nuclear blast; it would certainly be impossible with a homemade bomb on an oil tanker. So I immediately didn't buy it and I don't think the authorities would have either. A major flaw in an otherwise entertaining episode.
The other flaw is that there wasn't nearly enough Alexis in this one.