After you look at the top card to see if it's an action, and seeing that it is NOT an action, do you discard it or put it back? Surprisingly this is never clarified in the Guilds rule book or on the card!
The card is put back on top.
From the original rule book:
“Reveal” – when a player reveals a card, he shows a card to all players and then returns it to wherever it came from (unless instructed specifically to put it elsewhere). If the player is required to reveal cards from the top of his Deck, and he does not have enough cards, he shuffles in order to reveal the required number of cards.