Answer:
Roger Chilingworth's evil plan is revenge and he needs Hester to not reveal his identity for him to carry out his plan successfully.
Step-by-step explanation:
The Scarlet Letter, a historical romance fiction is a story of a woman, Hester who has a child with another man while her husband (Roger Chilinworth) was presumed to be lost at sea.
She is shamed and ridiculed publicly for adultery. Roger Chilingworth returns and plans to carry out his revenge on Hester's lover (Dimmesdale) by torturing and tormenting him. And he needs Hester to keep his identity a secret so as to achieve his revenge plan.