My travel companion and I laughed when we saw the name of this bar during the day. At night, we stumbled in and didn't realize it was the same place.
It was a solid if not intentional choice. The interior is clean with cute, retro decor. There is an interesting selection of drafts and a page of mixed shots on the back of the menu, both of which had many delicious options. The bartenders were diligent though not terribly friendly, but it was late and they probably wanted to go to sleep. I vaguely remember liking the music, but I wasn't sober enough to remember what specifically was playing.
There's a hair salon in Cambridge named plan b as well. I don't understand why you'd name your business that. It's like naming your kid Mediocre. I guess low expectations are easier to exceed?