Seeker of the Crown by Ruth Lauren

This book is about power. Princess Anastasia wants power and so does her cousin Inessa and they will stop at nothing to rule the two kingdoms. Younger sister Valor, daughter of the adviser to the Queen, saved her sister Sacha in the first instalment and she restored the valuable music box to Lady Olegevna which means peace should be restored between Demidova and Magadansky.  Then Valor overhears a conversation. Prince Anatol, who helped Valor and Sasha escape from the prison called Tyur'ma, is to be banished. Valor knows this is a terrible injustice and she knows who is orchestrating this - it is the evil Princess Anastasia. Queen Ana asks Valor to help. Sasha know she has to rescue Anatol and she will need help from her two best friends - Katia and Feliks. Then Queen Ana is kidnapped and the race is on to rescue the Queen and to save Demidova from certain war. 

Here is the bookseller blurb: One month has passed since Valor broke her twin sister Sasha out of the notorious prison Tyur'ma, but the girl who put her there to begin with--Princess Anastasia--has gone missing. The queen, desperate to find her daughter, asks Valor to track Anastasia down and bring her home. But just as Valor reunites with her loyal band of friends from Tyur'ma to begin the mission, the queen also disappears. If Valor can't restore order to the kingdom, it could mean that her new friends will be sent back to Tyur'ma . . . and her family torn apart. Once again, she will need to rely on people she can't quite trust, as well as her own instincts, to protect the people she holds dear. This thrilling sequel to the buzzy Prisoner of Ice and Snow is just as unputdownable as its predecessor, sweeping readers back into the vivid world of unforgettable protagonist Valor and her home of Demidova.

I loved Prisoner of Ice and Snow by Ruth Lauren - the first instalment in this series so I was excited to return to the world of Valor and her sister Sasha and the icy land of Demidova. Ruth Lauren does take care to recap events from the first book but I think you will enjoy this second instalment more if you take the time to read The Prisoner of Ice and Snow first. I think this series of two books will be thoroughly enjoyed by mature readers aged 10+. I enjoyed the first book more than the second but the world building, political intrigue, heroism, intelligence of Valor and 'girl power' in this kingdom made this a very enjoyable sequel.  Kirkus gave this second book a star review.