Harry Potter expected death to be the end of his journey. Instead, Death offered him a chance to make things right. But every reward carries a price, and Death shall be satisfied.
Harry had walked into the Forbidden Forest, and sacrificed himself to defeat Voldemort. He had been expecting to be welcomed by his loved ones in the next great adventure. Instead, he was being offered a reward for a feat he had unknowingly achieved, one he found to tempting to reject. Time-Travel. BEING REWRITTEN.
Lucius Malfoy's intention was to plant the diary amongst the youngest Weasley's textbook. He didn't account for the sharp eyes of the Boy-Who-Lived, now the diary was held in different hands.