By now, I am convinced that anything coming from Alice Oseman's mind is something everyone should read! After having read Heartstopper, Loveless and now Solitaire I consider Alice one of my favourite authors!
In this book we're getting to experience everyday life with Tori, Charlie's sister. And although this book came out before Heartstopper I, and probably many other people, started their journey into the Osemanverse with Heartstopper. That's why I was so excited to get to know Tori a bit better and see/read how her life is like. 
I think that Tori as a main character is very relatable and I could really understand the struggles Tori went through throughout the book. The way Alice writes about Tori's mental illness and how she deals and copes with it was very similar to my own experiences and I felt really seen in Tori as a character.
Of course, it was also very fun to see Charlie and Nick again in some scenes and I especially liked the scenes where Tori and Charlie were talking about their problems and how they were there for each other when no-one else was.
Of course, the romance that was also there, was actually very cute, and a thing I especially liked was how it wasn't treated like the romance we see in other stories. It was more like the story of a building friendship, we got to experience together with Tori and Michael, so you can actually say it's a friends-to-lovers romance, but also not, since the integral part of hhe story was Tori's way to finding herself.
This book was such a beautiful story and it was very delicately handled and that is what I love about Alice's writing! I am very excited to see what the future holds!