Van Dyck in Sicily: Painting and the Plague, 1624-25

In 1624, the 25-year-old Anthony van Dyck came to stay in Palermo, Sicily for a year, sketching the locals, hanging out with arty Flemish compatriots and taking on commissions for the portraits and grand devotional works that occupy the first two rooms of this brief but absorbing exhibition. There's a weirdly sultry, almost elfin-looking John the Baptist; a not entirely convincing version of St Stephen's martyrdom and a portrait of the island's viceroy, where Van Dyck managed to convey, really for the first time, that flattering combination of martial authority and slightly foppish elegance which led to his becoming one of the most sought-after painters of the age.

The viceroy himself, however, was dead within a year - a victim of the plague that was suddenly decimating the population. Not surprisingly, the tone of Van Dyck's paintings shifted, becoming more esoteric, more religiously ecstatic, with his five extant versions of St Rosalia - portrayed appealing to heaven on behalf of the stricken country - here occupying the final room. Saint Rosalia was an eleventh century hermit whose recently discovered relics were paraded through Palermo's streets as an apparently effective supernatural defence. At the same time, Van Dyck was working on establishing the iconography of the St- her golden tresses, wreath of roses and dull monastic tunic, experimenting with varying compositions and techniques, from the coldly ethereal to the more colourfully Rubenesque.

Unfortunately this show never quite teases out the most fascinating aspect of all this: that for the terrified patrons who commissioned them, these works weren't simply a portrayal of saintly intercession; rather, they were surely a form of intercession themselves - an offering of faith, a desperate appeal in the hope of salvation.