Ah, the power of reading! Because you already came across this legend, by sheer chance too, you are one of the few students who already know a little bit about the Chamber of Secrets.
You and Hermione fill Ron in. In sum, the Chamber was created by one of the Hogwarts founders, Salazar Slytherin, who did not agree with the rest of the founders about who should be admitted to study magic. Before he left, he made sure that the Chamber of Secrets could only be opened once his true heir came back to the school. Upon the heirs return, he would then open the Chamber once more, unleash the monster within and "purge" the school of those who were deemed unworthy by Salazar.
Ron looked as if he was hit by a troll's club. 'Monster?' he said in an abnormally high pitched voice.'You don't reckon it can be a...a big spider, do you?'
Somehow you doubt you would be that lucky. No, if that's the thing you heard whispering before, it will be something much much worse.