Diana Wynne Jones Dalemark Quartet Series 4 Books Collection Set (Cart and Cwidder, Drowned Ammet, The Spellcoats, The Crown of Dalemark):

Cart and Cwidder:
When twelve-year-old Moril’s father is murdered by soldiers, Moril inherits his ancient cwidder – a musical instrument with a mysterious past. As Moril and his siblings embark on a dangerous journey to escape the evil forces around them, he gradually learns how to channel the cwidder’s strange and powerful magic.

Drowned Ammet:
After his father mysteriously goes missing Mitt joins a group of freedom fighters plotting to overthrow the tyrannical ruler of Holand. But when his assassination attempt against the earl backfires, Mitt stows away on board a ship heading out to sea.

The Spellcoats:
Tanaqui and her family have always known they were somehow different from the other villagers. But when the great floods come and they are driven from their home, they begin to realise the part they must play in the destiny of the land.

The Crown of Dalemark:
‘Mitt arrived at the top of the steps, panting, and pushed open the door. “Oh, there you are,” said the Countess. “We want you to kill someone.”’Since his arrival in the North of Dalemark Mitt has become disillusioned. The North seems no more free than the Holand he fled, a fugitive accused of attempted murder.