The Fieldhouse Brothers, from Somerset, take on the Bueno Brothers, originally from Spain, in a closely fought first semi-final to build jaw-dropping chain reaction machines that will allow Richard to dust his ornaments without leaving bed. With a place in the final at stake and a challenge that requires delicacy and creativity, the contraptions need to be extra special. Chain reaction machine guru Zach Umperovitch is the expert judge and Shini Somara fills in the science behind the teams' eccentric contraptions.