Any Assassin may start the game hidden in one of the following units: Clanrats, Stormvermin, Night Runners, Skavenslaves and Gutter Runners.

Hidden Assassins are not placed on the table but are assumed to move with the unit they accompany. At the start of the game, secretly note down which unit they are hidden in. If the unit is wiped out or flees off the table before the Assassin is revealed then the Assassin is lost. Before he is revealed there is no other way an Assassin can be harmed.

Hidden Assassins can be revealed at the start of any friendly turn or at the start of any Close Combat phase. The owning player declares that his unit contains an Assassin and places the model where it can fight, displacing a normal rank-and-file model (not a character, champion, musician or standard bearer unless there are no other options). Displaced models go to the back of the unit.