While that may be an exaggeration, the deductive side of the series just doesn't operate as well without Waver's contributions. There's a lot to work with in this episode too, as in lieu of any action, we get a lot of new details surrounding the mystery. All of this is still presented in the jigsaw puzzle format this arc has employed, but pieces are gradually starting to come together.
So let's look at the pertinent facts of this episode:
Between all of this and other scenes shown over the past three episodes, I think the most reasonable conclusion is that the “heartless mage” is the mastermind and Hishiri is complicit. Having researched the last Grail War would give him a potential link both to Waver and Iskander, though why he's making this play is still up in the air, as is how Trisha fits into his scheme. Was she taken out just because her research was getting too close to something? That seems likely. It also seems likely that a play for a particular set of Mystic Eyes is being made, though whether it's Karabo's set or another is still uncertain, as is to what end (presumably involving the Grail War) it is meant to be used. Since Karabo has said that he's not fully in control of his Mystic Eyes and has a spotty memory, it's possible he was “eyejacked” into doing the murder through magic somehow. His Mystic Eyes turning out to be even more powerful than expected might be the solution to Trisha's premonition in episode 7 about a set of Rainbow Eyes coming up for auction.
The main mystery isn't the only interesting thing afoot. Gray's conversation with Hephastion in the episode's early stages, also seems loaded with meaning, both because of the comparison that Hephastion draws between herself and Gray and because of the further indicators of Gray's connection to Arturia. Hephastion labeling Gray specifically as a Sibyl is in reference to a flashback of Waver's lesson last episode, which suggests that she's at least partly channeling Arturia even if she isn't actually her Heroic Spirit. I'm not sure what to make yet of Hephastion also having Mystic Eyes; they seem too valuable to be just given to a Servant. Let's also not forget about the cool appearance of the Deputy Manager or the shout-out to Tsukihime and The Garden of Sinners by bringing up the Mystic Eyes of Death Perception as mythical items.
Overall, episode 10 remains clever enough to keep me enthusiastic about this mystery.