The gang goes drinking, Laika returns to her roots, and an unfamiliar face returns. Corona doesn't show up at all, because underage drinking would be a very serious matter. The title is that of a popular, sad song from 1931.
If Belka's line on the last page seems familiar to you from a certain anime that used it heavily, the Japanese isn't quite word-for-word identical to what you're thinking of. However, what Belka says actually matches the English a bit closer (in my opinion): 1) the pronoun she uses for herself is a lot more pompous, and 2) only Belka uses “いったい”, which is reasonable to translate as “…the hell…”.