You must be placing a 4th card to get rid of another.
Uncharted: The Board Game - The Adventure Begins June 2012
Type: Posts; User: Tylar_Bandai
You must be placing a 4th card to get rid of another.
All of your in play cards count towards the 3 card limitation.
You can also discard one of the basic cards, according to page 6 of the rulebook:
"If you would like to play a fourth card of that...