<p>Green Wing and Free Agents star Stephen Mangan is to play the lead role in BBC4&#39;s adaptation of the late Douglas Adams Dirk Gently&#39;s Holistic Detective Agency.　　Mangan will be joined by Darren Boyd as his sidekick Richard MacDuff and Cold Feet and Friends actor Helen Baxendale, as MacDuff&#39;s girlfriend Susan.　　Adapted by the Bafta-winning writer Howard Overman – who is also behind...</p>