The edges in these 4 graphs show the colour pairings of opposite
  faces of the cubes.<br />
  <br />
  To solve the problem combine all 4 graphs then look for 2
  subgraphs, one representing the colours on the front and back
  walls of the tower and the other representing the colours on the
  left and right hand walls of the tower, such that each contains
  all 4 colours and precisely one edge of each numbered cube.<br />
  <br />
  <br />
  <img src="/content/02/12/15plus4/clue2.gif" alt=
  "Clue for Instant Insanity" width="577" height="145" />