When Starbug crashes on a ocean planet, in a collison with a mysterious spacecraft. The Red Dwarf crew are soon aided by the pilot of the mysterious spacecraft, Ace Rimmer, a selfless and likeable Space Corps test pilot from an alternate reality, whose spacecraft, is a vehicle designed to travel across dimensions, as Ace travels from dimension to dimension, meeting many different versions of himself, including our Rimmer, whom has bitter feelings towards his alternate self from another dimension.