The Blood Stone by Jamila Gavin

Filippo has never seen his father. Before he was born, his father left their home in Venice to travel to the court of the Great Mogul Emperor Shah Jehan. He never returned. Twelve years later, a stranger brings a message that Filippo's father is in the hands of bandits, and only the most valuable jewel, his masterpiece The Ocean of the Moon, is worth enough to raise his ransom. Filippo follows his father's journey, into the intrigue of the Emperor's court, where Prince Aurangzeb plot to overthrow Shah Jehan. Filippo travels on into Afghanistan, to the bandit stronghold, and at last rescues his father. But it's too late. His father has been driven mad by his captivity and dies on the journey home. Filippo can hardly bear his loss, but finds his sadness healed when, years later, he returns to Hindustan with his brother. The Taj Mahal is a replica of The Ocean of the Moon; their father's work has not been in vain.