Fiona Bruce, Philip Mould and the team help Americans Kim and Chuck, who believe their landscape painting is by one of the founders of Impressionism, Alfred Sisley, building a case to prove its authenticity. Kim and Chuck bought the work at auction near Chicago and believe it to be genuine. However, the painting was turned down nearly 10 years ago by the authentication committee, so the team will have to find new evidence to persuade them to change their mind.