The speaker treats a very grand fantasy as if it were an ordinary night out. He takes Henry the Fourth to dinner, and it goes badly: he expected too much, and the king isn't pleased. So the speaker does the sensible, deflated thing and has a drink or two, then leaves. The title, "Faux pas," suggests he sees the evening as an embarrassing social slip, though the poem never says exactly what went wrong.
The second stanza turns strange and a little funny. A one-eyed cat walks along with him, and he asks it, "Strange fellow, tell me, how is the king now?" It's as though the cat might know, or as though he can't quite let go of the failed meal. The mood is dreamlike, wry and slightly lonely. The speaker sounds disappointed but gentle about it, and the question to the cat leaves a quiet sense that he still cares what the king thinks.