Scots accordionist Phil Cunningham journeys through Europe to perform with the finest Celtic musicians, from Irish star Sharon Shannon to charismatic Galician pipe player Carlos Núñez. On the way, he discovers how their once-threatened music is now thriving - and that the accordion has squeezed its way into the centre of their communities. In Cornwall, he joins hundreds of accordionists in the Obby Oss procession as the town of Padstow celebrates their ancient Mayday festival.