Still, there's something magical about the premise. It brings a certain clarity to mind. It distills the essential nature of what you're trying to achieve. So I would strongly suggest coming up with the premise of the novel at every stage of it. You'll probably be wrong the first few times. You might be wrong every time. But at the very least it'll help you regard your tale more clearly and consistently. It'll also help you prepare for the query writing phase.
This is the premise of the Butterfly Lady as I see it:
A web of conspiracy holds a small boy's fate in thrall, for his soul has been damned to a taint that slowly but surely turns him into a monster. Jason Arneil struggles to free himself from the lies and deception that threaten to damn him and, in doing so, must flee his island home and journey by ship to Port Vedic in the hope that someone there might discover a cure for his curse. But in that bustling city, he finds only answers that threaten madness and a desperate choice between two forms of damnation.