My original review was over the character limit so I'm editing it to be as blunt as possible. So here we go!
I don't think you spent too long on the potions. It's great when authors introduce these sorts of things early if they are important. JKR did it all the time so it's not only a good tactic, but also a natural fit in the HP world. It's far better than having a character just happen to know some obscure potion for no apparent reason. That would be too convenient to be realistic. You could have written some as if being read right from the book to just change it up a bit but it's not confusing or boring.
The towel scene. There is nothing wrong with having a little cliché now and then. One character walking in on the other in a state of undress is pretty much a staple in romance/chick-it. It's cute, fun, effective, and just plain works. For me, the part of this scene that didn't work as well was understanding Lily's motivation for pretending to seduce James and then trapping him in the blanket. Seeing as she knows he really likes her, it seems kind of cruel for the Lily you've created. I know she wants to know what he's up to but she doesn't even try to get the information by just asking him. It's a pretty extreme first option. Also, unrelated to the content of the scene, but you did do switch, from Lily to James. You're so close to the end of the scene, I would suggest leaving it all as Lily. There is nothing James is thinking we the reader have to know that moment.
Moving to Belle. I liked her introduction. I like that she's already been around a while; if Lily seems to like her/be at ease with her, even with her hot/cold demeanor, I as the reader feel ready to accept her. As with the potions, I think it's great you're introducing hints now at things to come later. It makes it more satisfying that way. Also, some long conversation where she suddenly blurts out her entire back story wouldn't be very palatable. Just a little at a time is a good way to go. Also, I don't have a problem with Sirius being drawn to a pretty girl. It's pretty normal to see a confident, handsome boy spending time with confident, pretty girl. Just as an aside, I loved her line about French versus confidence. Too clever!
It would have never occurred to me about the captainship/Dumbledore's reasoning if you hadn't pointed it out. I wouldn't worry about that at all. Who is to say these things weren't decided in September or October on occasion :)
Here are my initial thoughts on Alrek, the party and Lily's mistake. First, I like Alrek as a character for a lot of reasons.. First, I love the change in speech pattern he introduces. It really switches things up and though it sounds small, I think it has a big impact in this chapter. I like that he introduces conflict between Lily and James. And I like that I can already tell he has a "story" of his own. So I think he is great, no matter what else you have planned for him in future chapters. I also don't have a problem with Lily making a mistake. No matter what she's been through/how mature she is for her age, she is STILL a teenager. She won't always make smart choices. This one is pretty normal for teens her age, and I like that you are using it to show/develop character depth. Now to the party itself. I wouldn't go so far as to say it ruins the story. I really don't think it's that terrible a crime, I promise! However, of the three points, it's the hardest to swallow. Even if McGonagall allowed a party in some form, in truth, it would be supervised. Many students are underage. I just think back to how teachers in my high school wouldn't even let students inside classrooms without a teacher supervising. Obviously from the books we know Hogwarts isn't that strict but I would think a party, like a school dance or a Quidditch game, would just have to be supervised. I don't think without that, I could really "buy" into it fully. Obviously, that would throw a wrench into Lily's mistake, but even supervised, teenagers can find ways to get into trouble.
Okay, I know if I continue on in this much detail, I'll bump into my character limit so I'll lump a few things together here at the end. (1) I thought Remus using his own story to sooth Lily was very sweet. I can totally see him doing that. It was a great touch. (2) I love the idea of the Prospects. Did you invent that term? I don't remember it from canon but I love it. I do think it was a bit weird that Lily didn't feel super compelled to alert someone that a non-student was in the castle. I know you said you'd explain how later, which is fine, but with what is going in the world at large at the moment, I would think she'd feel compelled to tell/have a larger reaction. (3) The memory was touching and I like that it was triggered by smell. It's so amazing how even a hint of a smell can totally transport us. That said, I'm not a huge fan of time shifts in the middle of chapters. That isn't to say they are bad or that this one was done poorly. I just don't care for them as a style choice because I think they interrupt flow. When possible, I personally think it's better to keep them at the start or end of a chapter (unless it's part of a magic-y, pensieve thing).
Overall, I liked the chapter. I thought it was even better written than the previous three. It was just cleaner, crisper. A few general comments... (1) Obviously this chapter was long. I might consider keeping them under 8K in the future. I find that is where the validators start getting twitchy, which is (I think) a good indication of where readers might start to feel antsy as well...
Darn, I'm still out of room. I'll PM the rest of it to you right now :)
Author's Response: Ahh I didn't realize I switched to James at the end of that scene! Thank you for pointing that out! Why can't my brain stick with one character??? Haha
I don't think I realized what an extreme first option that really was, haha. In my head it played out more like she was planning to ask him, then when she got so embarrassed about him being in his towel, but then he wasn't embarrassed in the slightest. So him standing there looking arrogant kind of fed off of her desire to bring him down a notch. And considering she walked in on him, and he's been very kind, it isn't very nice of her, is it? Thank you so much for pointing that out, now that I'm looking at it from a new perspective I really don't love it.
I put in my message to you my thoughts about McGonagall. You have no idea how much my fingers are itching to edit that in now, haha! Of course I will give you credit for your help with this chapter, thank you so much for that idea ♥
Yay for Prospects! Keep an eye on the beginning of next chapter, you *may* pick something up. Though it's meant to be confusing, so you may not...
Maybe I can try and make Lily more persistent/urgent about it, they do go to his office to tell him the next day, but I see what you mean about her kind of acting like she just shrugged it off. Hmm... I'll have to play with that.
Ahh I'm sorry that time jump during the chapter kind of throws you, it is a reoccurring thing, I hope it doesn't drive you too crazy!!
Hahah I 'solemnly swear' no more chapters this long!
Thank you so much for giving me some new things to think about. This chapter is one that I've never been crazy about, and I think the addition of McGonagall at the party will help a lot, as well as playing with that towel scene a bit. Also! I'm happy you liked the introduction of Belle! I've had a few people automoaticly deem her a Mary-sue because she's pretty, so I'm excited that you're giving her a chance to see where she goes first. I can say that what they end up feeling for one another comes from a very strong part, and is something both of them really understand. This becomes a bit more clear in chapter 7. But I feel like it would have been unrealistic to make her a plain looking girl with nothing extreme about her. Like you said, Sirius is an attractive, confident young man. And in my head, he needs extremes. He's never happy being idle, he needs someone that pushes him. I'm kind of confident by the time all is said and done (if I can get you to keep your review thread open that long :P) you'll really love her.
Blah! I'm rambling! Seriously, your reviews are awesome. Thank you so much!