Looks like they're trying to make up for the sausage fest episode.

Our trio of lonely men is approached by two of their dormmates, who inform them of a plan to gather all remaining 'alive' students to defeat the Noushi Association. The plan is to attack the gate around 4pm, when the setting sun will make the Noushi unable to defend their boss. Calling themselves the Autonomous Dormitory Resistance, the two go off to round up more volunteers, but not without reminding our trio about the promised get-together with Hasegawa, Aoi, and Oikawa.

Too bad they never secured any confirmation of that.
Returning to the lab, our trio find all three girs dressed in leather. Much to the chagrin of all, the only one who still had a clean change of clothes was Hasegawa. Hearing a commotion outside, the trio head to the balcony to see some Noushi being chased by the other group interested in Itsuki's aphrodisiacs. However, the Noushi have laid a trap, resulting in those three losing their balloons and called 'out'.

Team Hasegawa

It's a trap!
Having witnessed this, our trio decides that they really need a plan. Later that day, the 'alive' students face the Noushi Association at the gate. The Noushi are unusually well prepared, and one of the leaders of the Autonomous Dormitory Resistance wonders if there's been a leak of information. He is not left to muse long, as both sides rush and the battle starts.

Hey, I haven't seen those microbes in a while…
All this while, Sawaki and crew are nowhere to be found. As the leaders become more and more alarmed, a cry is heard and Misato and Takuma race forward pushing a bag. Like a multi-stage rocket, Misato has his balloon popped, and Takuma takes over. When Takuma has his balloon popped, the bag is now within a few feet of the Noushi boss. (Gee, I wonder who's in it…)
The bag slowly unzips, and Sawaki pops out his head. As everyone watches, the boss slowly stands up, then smashes his fan into the ground, creating a small crater.

Oh shi-
Sawaki panicks and attempts to escape, but he is unable to free himself from the bag. However, the boss has mysteriously stopped, and shortly after some alarmed voices are heard from the left side. Sawaki looks over to see a team of Noushi scientists working a control panel, and it becomes clear that the 'boss' was really a robot. Taking this chance, Sawaki smashes the boss's balloon and retrieves the gate key from inside. A celebration ensues.

Wappo!
A Noushi hands Sawaki the 100,000 agri prize, and Professor Itsuki shows up almost instantly. Our trio immediately buys the aphrodisiacs, and rush to the lab. (Completely ignoring the baffled leaders of the Autonomous Dormitory Resistance.)
At the lab, our trio have 'innocently' set up the aphrodisiacs on a table in plain view. However, the first person to see them are Hasegawa, which she immediately identifies as 'Itsuki's aphrodisiacs. (Parade, raining, etc.) When the other two girls arrive, Hasegawa informs them what the aphrodisiacs are, and they refuse to try it. To everyone's surprise, however, Hasegawa suddenly consumes all the aphrodisiacs, apparently to show the guys that it has no effect. After the men leave, Professor Itsuki shows up and invites the girls out for sukiyaki, with the reason, "I somehow have 100,000 yen." (Haha, oh wow.) Hasegawa has research to finish, so she does not go along.

Innocent setup is innocent.

Hasegawa > aphrodisiacs
As Professor Itsuki, Oikawa, and Aoi head off, it is mentioned that Hasegawa becomes a completely different person when she drinks - which is why she does not. (Well, I wonder what's going to happen within the next 5 minutes?) Misato is drinking alone in his room, when Hasegawa shows up. Professor Itsuki had asked her to bring Misato some wines - some very, very, very expensive and good wines. Unable to resist, Hasegawa sits down to have a 'sip'.

Sure you will.
Meanwhile, Professor Itsuki has Aoi and Oikawa try the 'aphrodisiacs' as they eat. Neither notice any different, and say that aphrodisiacs must be 'dreams of ages past'.
Back at Misato's apartment, a drunk Hasegawa now has him in her clutches. It appears that Hasegawa's drunk side causes her to be batshit insane, and a poor Misato now fears for his life.

BAD END
Commuting back in a car, Aoi and Oikawa are now holding hands, and staring at each other suggestively. (Oh, my.) As the camera pans out, Professor Itsuki affirms the power of aphrodisiacs.

Unintended effect is unintended
The next morning, Takuma and Sawaki return to see a still-awake Misato (With claw marks on his face) cradling a sleeping Hasegawa in his lap. Mistao tells them to laugh at him for not being able to take advantage of the 'opportunity', but both the others agree that he did the smart thing. When Hasegawa wakes up, she finds Sawaki hanging form the ceiling, Takuma knocked out, and Misato with a pot over his head. Shocked and confused, she leaves wondering if she was the one who did it. After she leaves, the three relieved guys commend each other for diverting a disaster.

The 'aftermath' of Hasegawa's fury
Oikawa wakes up to see that she has been sleeping naked with Aoi, and her surprise is a testament to the effectiveness of Itsuki's aphrodisiac.

F-f-fanservice.
The episode ends with Sawaki still unable to contact Kei.

Thoughts:
Hmm, so who would've known the aphrodisiacs would work. As a result, we get a lot of fanservice this episode, including a (supposedly) post-lesbian scene. Our trio of idiots don't end up 'getting any', but such an outcome was to be expected. I notice that the series seems to be deviating a bit from the microbe theme, sure they throw in microbes here and there but it just doesn't seem to be the main attraction anymore. (Which is a problem, because I'm watching this series for the main attraction.)