Richiev:

My initial response was to the logline — a good sign for the general premise.

But after reading your synopsis, I would like to suggest that you rethink the status quo.

I think the decision to pass as a squirrel would work better in terms of motivation if Simon isn’t living the good life. Rather, the status quo for him is a Hobbesian existence, solitary, poor, nasty, brutish, and short. He’s living a ratty life where he faces one damn threat and aggravation after another: rat poison, traps, screaming humans, etc.

It’s his ratty life compared to the “good life” of the squirrels that plants the crazy solution in his mind and pushes him over the threshold.

Or you could double up on the motivation for him to cross the threshold with a carrot [love] and stick [jeopardy]. (Although I prefer the love story arising out of mistaken identity. It would kick in after he crosses the threshold.)

fwiw