Certainty

"Certainly, you do remember, Severus...?" "Yes, but it is a ridiculous thing to believe. We are no longer schoolboys after all, Lucius." "Ah, but that's where you're wrong." - Severus Snape is less than happy when he learns that Lucius will be staying at Hogwarts to watch the third task, but Lucius is determined to change his mind. Oneshot, LMSS slash, set in GoF