Britain’s premier art detectives, Bendor Grosvenor and Emma Dabiri, are on the hunt to find and restore one of the nation’s great lost masterpieces. Can a mysterious painting of a beautiful society woman really be by the celebrated artist Joshua Reynolds? And which celebrity playwright will lead them from Rome to Bath to London’s Royal Academy? With a fascinating treasure hunt into the art of the Georgians and a very modern 21st-century digital restoration, the results are truly spectacular.

Bendor traces the remarkable life of Sir Joshua from humble beginnings in the West Country to reach the pinnacle of the artistic establishment, becoming the first president of the Royal Academy and the country's most respected authority on art. In Rome, Bendor explores how Reynolds developed his style, known as the Grand Manner, and visiting the home of a private collector, he looks at a little-known self-portrait by Reynolds. Bendor explains why he believes it to be the greatest self-portrait ever made by a British artist, with virtuoso brushwork and a fluidity that gives it a remarkably modern appeal. Intensely personal and sympathetic, it was painted when Reynolds was at the height of his success, wealthy enough to buy a large house in the centre of London, lavishly furnished and adapted for his own needs. Bendor is also pleased to see the picture has many similarities to the portrait of Elizabeth Linley.

Emma explores the story of the man who donated the picture, Archibald McLellan, a wealthy businessman whose passion for art saw him amass an outstanding collection, which he left to the city of Glasgow.

Reynolds's achievements culminated with his presidency of the newly created Royal Academy of the Arts, a position he made his own and which gave him an authority to promote his own opinions about painting. The suite of rooms at Somerset House in the Strand, where the academy was originally housed, have recently been restored. Bendor visits it to get a taste of the spaces that would have been familiar to Reynolds, including the Great Room, where the tradition of the Summer Exhibition was born under Sir Joshua.

At the restoration studio, the portrait itself has been subject to close scrutiny. At some point in the last few years, the surface of the painting had been coated with a thick varnish, which has now discoloured and darkened. However, Reynolds's unorthodox painting methods, often using wax instead of oil to mix his paints, mean it must undergo stringent technical analysis to ensure it is safe to clean it. It soon becomes clear it will be impossible to restore the picture, which Bendor feels will damage the prospects of a favourable verdict from the Reynolds expert, Martin Postle.

Emma investigates the brief and tragic life of the woman who has always been the accepted subject of the picture, Elizabeth Linley. A child prodigy, she became a celebrity singer performing in her hometown of Bath from the age of nine. In her teens, she was regarded as a great beauty and suffered frequent but unwelcome attention from suitors. She eloped and married the playwright and politician Richard Brindsley Sheridan, and found herself at the centre of a constitutional crisis before her tragic early death at the age of 37. Emma is puzzled to know what evidence there is that the portrait is really Elizabeth, as there have been doubts expressed in the past. When she looks at some of Reynolds's vivid and insightful portraits of female celebrities from the Georgian era, she is surprised when she uncovers the true identity of the sitter in our portrait.

To give a sense of how the portrait would look if it had been possible to clean it, and to give his case a boost, Bendor creates a three-dimensional digital facsimile using laser scanning techniques and high-resolution re-colourisation. The portrait is returned to Glasgow for the verdict to be revealed. Show less