Hester Prynne's real husband, long thought to have been lost at sea, assumes the identify of Roger Chillingworth and practices medicine in Boston when he arrives in the town. During the time when his whereabouts were unknown, he was actually held captive by Indians; from them he learned much about natural remedies. He combines this knowledge with his strong scientific background to use herbs and plants in the medicines he administers, such as the potion he gives to baby Pearl when she is crying uncontrollably while Hester is still imprisoned.
When he sees his wife standing on the scafford holding a child that is not his, Chillingworth decides to conceal his true identity so that he can discover with whom Hester had her adulterous affair. He will singlemindedly pursue this quest throughout the novel until his curiosity is satisfied. Hester agrees to keep his secret just as she has determined to maintain the secret of the identity of her lover.