Dagon is all like 'yo' and Perry/you is all like 'sup'. Dagon needs you to destroy the human town of Innsmouth, but you're all like 'there are a lot of people living there, so I'mma need to get an army worthy of Mordor so I can simply walk into Innsmouth'. Dagon's all 'sure, but you have a time limit because that's how this game has replayability'.
At its heart, AoT:(N)ACDS is a coming-of-age tale about a boy/girl that is totally going to destroy humanity. By humanity, we mean a small coastal town. It is the Adventure-RPG based upon Shadow Over Innsmouth, where you control the eldritch horrors from beyond time and space! Inspired by classic RPGs, Lucasarts adventure games, and, you know, other cool stuff.