Overview: On a visit to Wales cycling scientist Adam Hart-Davis gets bogged down on the road to Holyhead. Fortunately, one of his heroes is the great road builder Thomas Telford, so Hart-Davis is able to rebuild the road using scientific principles. He also finds out more about the reclusive inventor who claimed his death ray could kill a rat at 64 feet; the bonesetters of Anglesey, whose extraordinary skill was passed down through four generations; and Robert Recorde who invented the equals sign. In Merthyr Tydfil, where the first railway locomotive was run 25 years before George Stephenson's Rocket. Hart-Davis celebrates its inventor, the Cornish wrestler Richard Trevithick.