Venice in the year 1295. Amidst the Ascension Day festivities, Teresa Fiolaro discovers an abandoned baby in a narrow canal. She calls him Paolo. Despite resistance from lier husband, Teresa raises the child in their home among the glass-makers of Murano. As Paolo grows up, his new parents realise that their son is short-sighted - but that this gives him a strange and acute eye for distinguishing colour and tone. Such a talent is recognised by Simone Martini, a painter from Siena, who sends Paolo on a quest to find the perfect ultramarine blue - the colour of heaven - a journey that will take him across the world, through Persia, Afghanistan, and China, in which lie learns not only about colour, but sight and distance, death and beauty, faith and love.