Girls' second season is officially in the home stretch, with only two episodes left after tonight's "It's Back," but the series remains as troubling and aimless — and somehow compulsively watchable — as its protagonist. I was frustrated by last week's episode, which introduced the laziest possible explanation for Jessa's various issues (and then sent her off to wherever TV characters go when the actresses who play them are too pregnant to hide it anymore). "It's Back" offers a similarly unexpected origin story for our heroine Hannah, who has apparently been battling severe obsessive-compulsive disorder since high school — and started to lose that battle sometime between last week's episode and tonight's.

Unfortunately, as with last week's major character development/plot dump, it doesn't totally work. This is arguably the most important thing we've learned so far about Hannah's past, and I'm not sure that "It's Back" gave such a significant revelation the time and the gravity that it needed. I can buy that Hannah has a debilitating condition that helps to explain and justify some of her personal baggage, and that the stress of her book deal could make her condition worse — but Girls wastes no time cranking Hannah's condition from zero up to 11. It's a little jarring to see Hannah obsessively counting door slams and potato chips just a week after an episode in which her biggest health problem was a UTI. This is not the first time that the show has dropped a series-altering bomb without warning. Hannah's book deal, which has been the engine driving the second half of Girls' second season, came out of nowhere: An editor from "Unpumped Magazine" — which Hannah apparently always loved, though somehow had never mentioned before — took her out to brunch and offered her a book deal. Lena Dunham is as close to a TV auteur as exists in the modern TV landscape, but Girls sometimes feels cramped, like the product of too many writers with too many ideas, each working too hard to squeeze them into episodes.

I bring this up because there's an important question that Girls will need to address going forward: Who and what is this show actually about? Looking beyond Hannah's OCD, which could easily have driven an entire episode, so much happened in "It's Back." Marnie stalked Charlie to his goofy new tech job. Adam had a promising first date. Shoshanna cheated on Ray with the doorman at a friend's apartment complex. None of these are bad storylines in principle, but they each have something in common: They were introduced within this episode. At this point, there's very little connective tissue from episode to episode. While that pattern has allowed Girls to go to some fascinating and unexpected places, it has come at a significant cost to the show's overall narrative momentum.

It wasn't always like this. The first season, which seemed at first glance to be aimless, actually had two well-conceived structural storylines that held the entire season together: Hannah's beguiling relationship with Adam, and Hannah's attempt to survive without her parents' financial help. How has Hannah continued to pay for her apartment now that she's kicked Elijah out? It's not clear. When did Charlie get interested in making iPhone apps? No idea. Weren't he and Ray in a band together? Yes, and they were also best friends — two plotlines that have been dropped altogether this season. Girls isn't in danger of cancellation — in fact, it's already been renewed for a 12-episode third season – but I wonder if the show has begun to lose its focus, and a portion of its audience along with it. (Last week's episode garnered the lowest ratings in the series' history.)

In one of the best scenes in "It's Back," Ray advises Marnie to turn her potential energy into kinetic energy — advice I would pass on to Lena Dunham and the rest of Girls' creative team. The ideas, the writing, and the performances on this show remain very strong, but as the season draws to a close, I'd much prefer to see Girls tackle a single character or idea with a lot of conviction, instead of half-heartedly toying with story ideas for an episode or two at a time. There's so much that works about Girls. It just needs to follow through.

Read more Girls recaps:

Girls recap: A disastrous trip outside Brooklyn

Girls recap: A night out with the boys

* Girls recap: 'One Man's Trash'

Girls recap: 'It's a Shame About Ray'

Girls recap: Hannah the antihero

Girls recap: 'I Get Ideas'

HBO's Girls season 2 premiere: Almost getting it kind of together