The Thickety: The Last Spell (Book 4), J.A. White

Kara and Taff have discovered that the Spider Queen is searching for Princess Evangeline’s grimoire. But this isn’t any grimiore - it is the Vulkera, the first grimoire ever made. Legends say it holds special powers and that any witch who wields its dangerous magic would be indestructible. 

But the Vulkera has been hidden for centuries. Long ago, the grimoire was divided into four sections called grimes, and the pieces were carefully concealed across Sentium. The Spider Queen wants to bind the grims together to regain the Vulkera’s power . . . and use the ancient weapon to destroy everything. The greater the spell, the greater the cost. 

Kara and Taff have to find the grims before it is too late. Accompanied by an unexpected companion, they will travel through time, come face-to-face with the creatures that guard the grims, and unravel a king’s dangerous secret, before one final battle against the Spider Queen. Kara knows that everything that has happened since the day she stepped into the Thickety all leads up to this. It is her last chance to save the people she loves. And to cast a spell that could change magic forever.