It's quite the experience to reread CoS after HBP.
1. Harry *is* a Horcrux. An unintentional one, perhaps, caused by Riddle's killed Lily, but he is one. *Dumbledore* says so when he explains why Harry's a Parselmouth.
2. Sexuality is starting to play a big role in this book. Hermione, who is thirteen and female, is in the middle of her first crush. Too bad it's on someone who will never love anyone as much as he loves himself, and who is as deep as one of his photographs. Harry and Ron, being twelve and male, find it all hysterical.
Lockhart also introduces sexuality by holding that Valentine's Day idiocy. Everyone was annoyed and poor Ginny was embarrassed (but she wrote that poem anyway, and I don't think Tom made her do it.) This is one of the things that bothers me - Ginny is *eleven*, and she starts her crush on Harry at ten. I don't like that she's sexualized that young.
3. The Mandrakes are even more disturbing now, and they were disturbing on the very first reading. The students and Mrs Norris are Petrified, and the only way to save them is to take the Mandrakes just as they reach sexual maturity (trying to move into each other's pots) and cut them up and stew them down.
The Wizarding world is frozen, Petrified. It's going to be saved by a bunch of adolescents who are now entering sexual maturity. Will they also be destroyed?
4. Lucius decided to do this all on his own. I don't think he wanted Tom back in power, and, for a wonder, I don't think he knew it would kill Ginny when he slipped the book into her cauldron. I think he's capable of that - he truly hates Arthur Weasley - but I think his motivations were something else. He knew that the Chamber would be opened. He believed that would cause Dumbledore's ouster, and possibly even close Hogwarts, thereby destroying Dumbledore's influence on the wizarding world. He also, at the very least, risked the lives of the Muggle-born students as well as Ginny's, but that would be of limited concern to him. He was using the diary to get power himself. He certainly didn't know it contained a bit of his Master's soul. That's just not the sort of thing Riddle would let slip.
Riddle isn't getting Lucius out of Azkaban any time soon.