The Swansea museum store contains everything from a stuffed pigeon to a police car, but can Bendor and Jacky reveal a multi-million pound lost masterpiece that will not only become a jewel of Swansea museum's collection, but also rewrite art history?

Art experts Jacky Klein and Dr Bendor Grosvenor visit our most diverse and fascinating museums as they track down previously unknown paintings by some of the world's great artists. Haddo House is one of Britain's most northerly stately homes. Tucked away in the wilds of Aberdeenshire, it has been home to prime ministers and earls - but is it also home to some of Scotland's greatest lost paintings? Nearby, in the storerooms of the Montrose Museum lies a mystery painting with a giant hole in it.

Bendor and Jacky visit the Ulster Museum to investigate what have long been disregarded as low-value copies of works by Flemish artist Peter Breughel the Younger.

Pollok House is a country house right in the middle of a Glasgow city park, bordered on one side by the M77 and on the other side by the south side of Glasgow. It is owned by Glasgow City Council and looked after by the National Trust for Scotland.

Along with a hippo skeleton, a stuffed hedgehog and a log boat, Derby Museum has the best collection of Joseph Wright of Derby paintings in the world. Wright of Derby is one of the greatest English artists who ever lived.

Carmarthenshire County Museum is a slice of history in itself. The building that houses it has been in continuous use since the 13th century. Once a bishop's palace, it was where the Bible was first translated into Welsh.

Hospitalfield House in the fishing town of Arbroath on Scotland's east coast is a Victorian treasure trove. The couple who owned this great house back in the 19th century were obsessed with the decorative arts.

Dr Bendor Grosvenor discovers a small portrait of Rembrandt in the collection of a National Trust house, Knightshayes Court in Tiverton, Devon. The painting is thought to be a later copy of a self-portrait by Rembrandt now in the Rijksmuseum in Amsterdam, but Bendor believes it is in fact a study for the finished picture by Rembrandt himself.

At the Manchester Art Gallery, Dr Bendor Grosvenor discovers a painting of a country gentleman from the 1770s which he believes has been wrongly attributed to Nathaniel Dance. He feels sure it is in fact by the German painter Johann Zoffany, a favourite portraitist of the royal family under King George III.

Petworth House in West Sussex is one of the great Baroque treasure houses of England, and Dr Bendor Grosvenor finds two paintings which he feels warrant investigation: a portrait of a lady from Genoa which was once attributed to Rubens, but Bendor is convinced is by Anthony van Dyck, and a portrait of a young cardinal in the style of Titian, which Bendor believes may be by Titian himself.

A potential portrait by Pompeo Batoni is investigated.

Potential landscapes by Thomas Gainsborough, Jan Brueghel the Younger and Joos de Momper are investigated.

A potential painting by Sandro Botticelli is investigated.

Potential portraits by Francesco Trevisani and Joos van Cleve are investigated.

A potential portrait by either Parmigianino or Francesco Salviati is investigated.

Technical difficulties frustrate Bendor’s attempt to uncover who painted an unfinished portrait in a Glasgow museum. Emma reveals the true identity of the sitter after 300 years.