The Science Club questline? It starts from the Computer Club questline. The Computer Club is next to the Staff Room. You just keep going back to the Science Club's lab once the questline starts. If you mean what you need for the Good End, then Serena needs to remain sane through the mindbreaking scene. I used the relevant amulet myself (see the Desire Shop for amulets), but have been told that no longer works, so you probably need maximum sanity and perhaps a sufficient succubus level/powers. Standard RPG stuff!