A character built on composure spends the climax losing it in the least composed way imaginable. This week the investigation gets so thick you could spread it on toast. Of all the things said this week, "I was once a teacher, you know." is the one that will follow you to bed. Long-time viewers get a payoff: "So he might have had another, secret lab?" is no longer a mystery. A rough one; the next episode owes you.