Harry left to follow the voice. Later he would come back with Tom Riddle's diary. As soon as Harry left, Draco got up from the Slytherin table, and walked up to the Ravenclaw table.
"Granger," he walked up to her. She turned back to see who called her.
"Malfoy," she greeted him as unenthusiastically as he had.
"May I have a word with you?"
Hermione hesitated, but then got up and walked with him. Once they got far enough from everyone, he turned towards.
"I need to ask you a favor."
Hermione raised her brows in surprise.
"It's about Harry…" Draco added.
"What's up?"
"You need to talk some sense into him. He's not listening to me, but maybe to you he would…" Draco said, and then elaborated, "he keeps getting himself into undesirable situations. People think he's the heir of Slytherin, and instead of staying out of trouble, he keeps running towards it."
"Do you think he is the heir of Slytherin?" Hermione had to ask.
"What?! No!"
"Are you?"
"Also no, and if I were, I wouldn't tell you."
"You do hate muggle-borns."
"I don't!" Draco said unconvincingly. "Anyways, just please! Help me keep him out of trouble?"
"I'm doing it for Harry. Not for you."
When Draco saw Tom Riddle's diary later that day, he immediately recognized it. That's the diary that opens the Chamber of Secrets. His father gave it to Ginny Weasley in Flourish and Blotts.
"This is clearly dark magic. You should take it back to Moaning Myrtle's bathroom immediately." He warned Harry. Harry obviously refused. He had to do something about it.
That night, while Harry was asleep, Draco stole the diary. The next day he bumped into Ginny Weasley, making her drop the books she was carrying and, very sneakily, slipped the diary into the pile of books on the ground.
He stood up. Brushed off his clothes. "Watch where you're walking, Weasley!" He snorted, and walked away.