The cubes were a species of biomechanoid hybrids from another dimension. Their dimension was extremely cold, which caused many of them to explode due to the extreme heat they experienced when they crossed dimensions to Nevada, USA. The Seventh Doctor, Elizabeth Klein and Major Wyland-Jones devised a plan to use flamethrowers in conjunction with gales caused by the Skyheads to make them retreat back into their dimension. However, the cubes instead joined with each other to form a giant cube in an attempt to blow the dimensional corridor open. (AUDIO: Dominion)