The presence of William Bell's consciousness in Olivia's body threatens to displace her mind permanently, unless Walter and Peter take extreme measures.
Hmph. That was the first episode in a long time that I actively disliked. It felt like a Fringe fan film: the writing was awkward, the plot rapidly became silly, and the animation, while fun for the director and the only way you'd get William Bell back on screen, felt pointless.
The whole "disembodied William Bell" storyline seems like a needless subplot. Glad to see they're back to the broad story arc next episode.
I've never been a fan of the whole scifi cliche of the idea that someone's mind is represented metaphorically by a convenient action setpiece. There were some nice bits of foreshadowing sprinkled in though.
Also, they blew the alcohol; ethyl is the one you're supposed to drink, methyl alcohol is toxic and causes blindness.