Really, this is clearly the cleverest series to have come out this season. Kaiba may be good at other points, but Himitsu is a master in dropping hints that might solve the mystery. This series really draws you in like no other, also with the help of the terrific soundtrack. You really need to watch an episode at least twice in order to fully understand it.
The way the creators also revealed that Nanako fancies Aoki was also quite creative. Most series just show a very obvious and unsubtle blush, though Nanako instead just misses her chair, and you can also constant see her around Aoki, without him noticing it.
And the theme of this episode… it was really pushing taboos, as it reflected an issue of modern society that even Sayonara Zetsubou-Sensei didn’t want to enter: the bother that elder people are to their younger generations. The culprit is a guy who ritualistically kills off older people who aren’t wanted by their families due to poverty. That one scene where the kid asks when he can get his own room: “you’ll get your room as soon as grandfather dies”. “Oh, I hope he dies soon then”.
On a side-note: there’s something I’ve been wondering. It rather annoys me a bit how many people are dismissing this series because it looks “gay” (what’s wrong with homosexuals anyway?). But at the same time, you don’t hear anyone saying this about Death Note (a series that shows quite a few similarities with Himitsu, by the way), even though that too featured a number of *ahem*”bishies”, that even ended up washing each other’s feet at one point.