A private army run by the so-called Wagner group is fighting on Russia's behalf in Ukraine, but is the group's leader and his soldiers becoming a problem for Vladimir Putin?David Aaronovitch is joined by a team of experts to find out more about the Wagner group - the mysterious private organisation that's acknowledged by the Russian government to have been supplying soldiers to fight its war in Ukraine. Wagner's leader, Yevgheny Prigozhin, was once known as Vladimir Putin's 'chef' after providing catering services to the Kremlin. Now, soldiers fighting for him are responsible for one of the few Russian military successes in Ukraine in recent months. Has this prowess on the battlefield re-invigorated Russia's army - or turned Prigozhin into a potential rival to President Putin?