Oikawa (or rather, "Team Oikawa") might still be concerning herself with the mystery of the hidden underground passage, but away from this it seems that Haruka has something even more vital on her plate.
Such are her worries about her future, as her father threatens to drag her away from her research with an eye towards an arranged marriage, that she largely ditches her work for the time being, leaving the other's to pick up the miso-making slack - a decision that at least grants us another of this show's cute little educational segments to explain said process via a kind of idiot's guide.
After a breather in the form of a trip to see the grand (or not so grand) re-opening of the Hiyoshi Liquor Store under the iron fist and smart ideas of Kei, returning to their work sees Oikawa and company run into Haruka. While she fills her junior's head with ideas about just what the hidden passage that Oikawa is fascinated with could contain, a serendipitous opportunity presents itself, as said secret passage is open for all and sundry to see. What horrors lurk in the cellar beneath the laboratory? How about some beer? This anti-climax sends Oikawa into a depression that seems to spur Sawaki on to finally spill his secret with her...
Perhaps in keeping with Oikawa's own sense of disappointment, this week's Moyashimon Returns did feel like a bit of an anti-climax - it somehow seemed to lose a little of its energy in terms of humour and characterisation, and while I still enjoyed its educational elements greatly there wasn't really anything to shout about throughout most of the episode beyond that. Then again, given the delicious "cliff-hanger" to the episode and all it might entail for Sawaki and Oikawa's relationship going forward, it seems like we'll have no such concerns about nothing noteworthy happening in next week's episode.