The nuns in the chapel of the Carmelite convent at Lisieux are out of sight as pilgrims join them for morning Mass. Only their voices can be heard from behind the grille that divides off the church. Their singing adds a vigour and sweetness to the otherwise faltering and occasionally flat responses of the rest of us. 

They are not the only ghosts at this feast. Alongside the nave, next to the nuns' enclosure, is another area, this time plainly and by design open to view by the whole congregation. It is dominated by an elevated and elaborate gold casket with plate windows, like the rear part of an outsized hearse. This extraordinary object contains something bizarre — a life-size model of Saint Thérèse of Lisieux, the nun who died here at the age of 24 in 1897, and whose cult within Catholicism has spread around the globe from this otherwise undistinguished small town in the Pays d'Auge region of Normandy. 

The plaster Thérèse is dressed in the brown and white robes of a Carmelite. Her left hand lies on her chest, clutching a crucifix, while her head rests on a grey pillow and turns towards the main body of the church. Undistinguished, even saccharine as a work of art, this statue does nevertheless have an extraordinary life-like quality about it, never more so than during Mass when I repeatedly glance over at it and Thérèse's smile, though her eyes are closed, seems to be directed at each and every person in the pews. 

Underneath the memorial lies a reliquary containing the bones of the saint, placed here after her grave was exhumed in 1923. Or, to be more precise, some of her bones. Others, taken from her coffin, are elsewhere. Her right arm, for example, is on display in a glass case at the other end of Lisieux, in the great white basilica with its mosaic interior that was opened in the 1930s to accommodate the 800,000 pilgrims who come here each year. One tiny fragment of bone was carried into space in 2008 by the American astronaut, Ronald Garan, on the space shuttle Discovery. And other, more substantial portions of her limbs have been placed in two separate reliquaries — one bigger than the other — which after the Second World War began touring France, and which, since 1996, have travelled to more than 40 other countries, from Iraq to Australia. Later this month, one of them is coming to England, where it will go on display as the centrepiece of prayer vigils in various Catholic cathedrals, Carmelite churches, one prison chapel (Wormwood Scrubs) and — an ecumenical first for Thérèse — the Anglican York Minster. 

The veneration of saints' relics was commonplace in pre-Reformation Europe. An abbey keen to thrive in medieval times benefited from the possession of relics which helped to draw pilgrims in search of miraculous cures. Lindisfarne, for example, put on display the incorrupt remains of its seventh-century bishop, Cuthbert, while Canterbury housed the shrine of the murdered Thomas à Becket.