The Lighthouse at the World’s End by Amy Sparkes

Adventurous, magical and brilliantly funny final book in the House at the Edge of Magic series.
Nine and her friends are headed to the mortal realm in search of the only thing that will shake a very tricky witch off their a priceless stargold locket. It lies hidden in the Nest of a Thousand Treasures, guarded by Nine’s old foe – the formidable gangmaster of all the thieflings in London.

Even if Nine can get her hands on the locket, the friends must find a way to release its power – and for that they must travel through the World Between Worlds to the lighthouse on the Isle of Illusion, where nothing is quite as it seems…