Seeking GM advice, tricking players into helping the villian

I’m looking for a little help and guidance as I’m trying to plan out my first attempt at gm’ing.

My basic idea for a plot:
The new adventuring group in a Tabaxi town are hired by the towns mayor to solve various ill’s befalling the place. I’m planning on starting them off at LV1 and using his quests to build the players up to about 4-5.

The thing is, I want the mayor to secretly trying to destroy his own town as sacrifice to his evil deity (in order to receive a blessing and become a Rakshasa).

What sort of quests could I give to the players intermingled with ordinary quests that would eventually lead to plague, famine, invasions and various calamities that would ultimately end the town?