Scarlet is a book that divede its points of view between Cinder's situation and a new girl: Scarlet. As the first book end start the second: the reader will see Cinder quite soon but Scarlet moments aren't less interesting. 
 The action is basically everywhere. If in the first book, Meyer takes her time with Cinder, with Scarlet the cyborg bounce into action with a magistral escape from the prision where she is detained and during her path she meets Throne, a character well loved by the TLC fandom. And I cannot deny that he's quite fun - still not my favorite, anyway. 
 But, as I was writing, Scarlet is the other protagonist of the story but her narrative take plance in France, from the other side of the world in respect of Cinder's location. With her there will be a strange street fighter: Wolf. 
 In my opinion, Scarlet is a big improvement from the firt book. Many points that lacked of logic here are completely absent and the worldbuilding goes on without a great numbers of questions, even if the ones from the first book still reamains without answers. 
 So, Scarlet make the series take its great leap with the whole story, but it still lacks of details. Let me make an example: I can feel the world, this sci-fi new world full of tecnology and a new political and power system, but still... I need more disclosure. 
 I get that it's not the point of the whole story, which concentrates around the characters and the mistery that surround the Lunars, but still I would love to scream: I needed more! 
 The so famous Lunars finally make their entrace... and so yes, a bit of question arise here and here: 
 - why Lunars are, well, Lunars? 
 - How did they arrived to live onto the Moon? 
 Talking about the girls... they're both good. Cinder start to get out her inner strenght and Scarlet is basically born bursting out her agressive nature - thanks her grandma. I liked how Scarlet characters is coherent with her image. She made many risking decision without thinking that much, being totally impulsive and sometime clueless, but it's normal since she never left Rieux before and the town where she grow up is nothing more than a village. 
 About Wolf I don't feel to write much about, since I think that Meyer write her best of him in the next books. 
 If you had hard time with Cinder, Scarlet will possibly change your perspective and lead you directly to Cress, so I can sugges to not all so eager fan of TLC to do not give up.