The hero cannot be seen. However, the character has not vanished into thin air and can still be heard, smelled, and touched. You may attack an invisible character only if you are aware of the character’s presence and approximate location. To locate an invisible character, make a competitive skill check on Perception (Search) vs. Stealth (Sneak). If successful, you may attack (and defend against) the invisible character with the following restrictions. Your attack values are halved, and ranged combat is much harder (roll a 1 on 1D20 to succeed), as is a successful defense (again, roll a 1 on 1D20). You may not defend against an invisible character’s ranged attacks. Characters must touch invisible opponents to affect them with spells or liturgical chants.
Publication: Core Rules page 36