It's effectively a one-picture exhibition at Norwich Castle — but oh, what a picture. IAN COLLINS is transfixed by Titian's Diana and Actaeon, saved for the nation at a cost of �50m.

During the Second World War the National Gallery had a cultural heyday when it was largely closed down. Crowds flocked to lunchtime concerts at which Myra Hess orchestrated a heroic programme of German music drowning out the Blitz, and from safe storage in a Welsh mine art treasures were returned for very popular showings in Trafalgar Square one at a time.

These days we are bombarded with images and generally spoiled for sensory choice. And the world of virtuality is posing such a threat to vision that many people scarcely look at all (and very rarely out of a window).

Now, more than ever, it's good to focus. I often nip into the National Gallery to savour a single picture — my favourites including the Doge Leonardo Loredan portrait by Giovanni Bellini, Stubbs' Whistlejacket and Titian's The Death of Actaeon.

The last of these, first seen on a TV screen when saved for the nation after a political and financial struggle of 1971, alerted me as a teenager to the great adventure of art.

The sheer drama of its composition rendered in a frenzied brushwork far more vivid than a photograph, for a scene showing Actaeon the huntsman turned into a stag by Diana and torn apart by his own hounds, thrilled even on a black and white telly.

Well, now all of East Anglia needs alerting to a singular Titian treat with the arrival in our midst of a further work in a most wonderful cycle.

Diana and Actaeon is another of the six large mythologies — three of them depicting the same myth and all dubbed 'poesies' or visual poems — created by the Venetian master in the middle of the 16th century. In 2009 it was bought jointly by the National Gallery and the National Galleries of Scotland for a whopping �50m.

The Scottish Government, National Heritage Memorial Fund, Monument Trust (one of the Sainsbury family charities) and Art Fund all made big donations, on top of thousands of smaller ones from individual art lovers all over the UK.

The precious prize is now in Norwich, pending visits to Liverpool and Cardiff, in the run-up to a centrepiece role in the National Gallery blockbuster Metamorphosis: Titian 2012.

There are several adventures to relate here – starting with the inspirational story. The Roman writer Ovid tells in his Metamorphoses of a young noble who is separated from his pals after a day's stag-hunting, and chances upon Diana, chaste goddess of the hunt, bathing with her attendants in a woodland pool.

The upstart mortal will suffer a terrible fate for daring to disturb the gods. The follow-on image of Diana and Callisto (saved just last week for �45m) shows the pregnancy of one of the goddess's nymphs by Jupiter brutally exposed and the third shows the slaughter of the hapless mortal. The next adventure, now to be pursued in Norwich, is the sublime way in which Titian reveals the initial scene. The fated hunter stumbles upon the virginal bathers, with some of the nymphs apparently far from alarmed or appalled by the intrusion.

Alas he is already too mesmerised to read that look on the face of Diana which really should have had him turning on his heels. And how docile that hound which will soon join a pack of divinely commanded assassins.

A work of huge scale, ambition and electrifying energy, the erotic painting is a sumptuous study of earth, cloth, tree, air and water, wrought with brilliant pools of orange, pink, red and blue and with a startling focus on naked flesh.

One of six of the best works of the Italian Renaissance commissioned from Titian by the mighty Philip II of Spain from 1549, this one was nearing completion nearly a decade later when the monarch was married to Queen Mary of England – and when her pregnancy was already found to be of the phantom variety, and the Protestant-burning ruler was herself heading for an early grave.

Many years later, in 1588, her widower would launch his Armada after Elizabeth had executed Mary Queen of Scots to secure a Protestant succession. Well, fleet-wrecking wind and wave really held the religious line so that an old and very worldly Catholic king stayed put in Madrid with his prized painting.

In 1623 when Prince Charles of England and Scotland — soon to be Charles I — was in Spain to woo the Infanta, the masterpiece was packed up as a diplomatic gift. Then the engagement went awry and the present was unwrapped and put back on the wall — to be covered up due to all that daring nudity every time the queen was about to pass by.

In 1704 Philip V presented the painting and the sister work Diana and Callisto to the French ambassador, and soon they had passed to the magnificent collection of the Duc d'Orleans in the Palais Royal, where they remained until the French Revolution.

Shipped to England in 1793, they were owned by the Duke of Bridgewater, then Lord Gower, then the Earl of Ellesmere – hanging in Cleveland House in Pall Mall, just along from the National Gallery, where rather ironically they remained on public display until towards the end of the Second World War. Then they were removed and lodged on long-term loan with the National Gallery of Scotland.

These pictures by a master whose 70-year career ended with his death in 1576 have had a huge impact on western art — greatly influencing Vel�squez, Poussin, Rubens, Rembrandt, Constable and C�zanne. The Castle show underlines the point with a Diana and Actaeon after Titian oil sketch by the Norwich School's Joseph Clover, Cornelius van Poelenburgh's Landscape with Roman Ruins to represent Titian's influence on Dutch Italianate landscape painting of the 17th century, two 1980s oil sketches by John Lessore and 21st century photographs by Tom Hunter.

When Lucian Freud had an exhibition in Edinburgh he made haste to see the Titians, admiring the master of paint in general and of painted flesh in particular.

'How is it that these paintings, which are as effortless as a Matisse, affect you more than any tragedy?' he asked.

And then he answered: 'Everything they contain is there for the viewer's pleasure.'

? Diana and Actaeon can be seen at Norwich Castle until April 15, Mon-Sat 10am-4.30pm, Sun 1-4.30pm. Museum admission �6.60 (�5.60 cons), but a Titian special is available for �2 (�1 cons). Pop in for a Pound tickets are available daily one hour before closing time. More details on 01603 493625, www.museums.norfolk.gov.uk

SAVED BY YOU

One of the UK's most important privately owned Old Masters, Titian's Diana and Actaeon was bought for the nation in 2009 after an emergency appeal raised �50m in little over four months.

The painting, which was the centrepiece of the world's finest collection of Old Masters in private hands, the Bridgewater collection, is now jointly owned by the National Galleries of Scotland and the National Gallery in London.

The appeal was launched after the collection's owner, the Duke of Sutherland, offered to sell the painting and its companion picture, Diana and Callista, to the nation for �100m.

The �50m price – well below its expected value on the world art market – made the acquisition the largest ever public purchase of a single work of art in the UK ever.

The campaign to buy the second painting Diana and Callisto, which depicts a nymph, impregnated by the god Jupiter, being expelled by the goddess, finally succeeded this month at the price of �45m.