Dobby appears in Harry’s bedroom and tells Harry that his life will be in danger if he returns to Hogwarts for his second year.
Between his excitement about meeting Harry, his sense of urgency in his mission to warn him, his astonishment at Harry’s kindness, and his guilt and fear of returning to Malfoy Manor, Dobby works himself into a noisy emotional frenzy before he is able to explain anything to Harry. After his racket causes Uncle Vernon to interrupt and tell Harry to be quiet (while Dobby hides in the closet), Dobby accidentally reveals that he has been intercepting Harry’s mail all summer. Doby, in fact, has Harry’s mail with him now and promises to give it to Harry if the boy will agree to not go back to Hogwarts. When Harry refuses to agree to this bargain, Dobby ruins Aunt Petunia’s pudding and then disappears (CS2).
Harry discovers Dobby in his bedroom slightly after 7:30 in the evening (CS1).
Of his misguided attempt to protect Harry by blocking his mail, Dobby says he "did it for the best - " (CS2). In retrospect, this seems to anticipate DH's broad critique of "for the greater good" justifications. -BB