One of Our Spies Is Missing (1966)

Someone is using cats in experiments to develop a machine that can reverse the aging process, meanwhile a famous scientist (Dr Lancer) has gone missing, only for him to reappear looking 30 years younger. UNCLE agents Napoleon Solo and Illya Kuryakin are sent to investigate the plot in Europe - Illya is sent to London to discover who is abducting cats while Solo travels to Paris where Dr Lancer's daughter is working as a fashion model. They uncover a plot by female members of the fashion business to develop the anti-aging machine for their own use, however the suave THRUSH agent Jordin has other plans. Thus a race begins between UNCLE and THRUSH to take control of the machine.