The way I look at it, most of what came before the introduction of Armitage is backstory, since he's the hero. Doesn't make it irrelevant, far from it, but means this is REALLY the beginning of the action.
Don't worry - I cram as much of the backstory back in as I can.
And now I have Innsmouth haunting my brain. Came up with a super creepy way to present it.