The object of the game is to build tunnels to bombs and bring them back to your home base.
The bombs have various effects hidden on their base. The tunnels are built through tile laying, so each player (best played with four) digs furiously from his manhole in the corner towards the bombs, hoping to reach 'em first. If you connect tunnels, then you'll be able to try to steal another player's bomb before he brings it home.
The basic turn goes like this:
First, you move your pawn to another tunnel tile.
Second, if you ended up or started on a bomb, test (with a special die) to see if it blows up.
Third, draw a tunnel tile (you have a hand of four) and play one.
Finally, if you get a bomb home safely, read its message.
In addition to the tunnel tiles, there are white, black and grey spy tiles. They are used to block tunnel tiles (each tunnel tile has a little black or white spy drawn in its middle, so you can play a White Spy only on black tunnel tiles and vice-versa; the Grey Spy can be played on either).