Spy
Type Action - Attack Effect +1 Card, +1 Action, Each player (including you) reveals the top card of his deck and either discards it or puts it back, your choice. Cost 4 Coins Set Dominion: Base Set Illustration Michael Menzel

Additional Rules from the RulebookEdit

Spy causes all players, including the one who played it, to reveal the top card of their Deck. Note that you draw your card for playing Spy before any cards are revealed. Anyone who does not have any cards left in their Deck shuffles in order to have something to reveal. Anyone who still has no cards to reveal doesn't reveal one. If players care about the order in which things happen for this, you do yourself first, then each other player in turn order. Revealed cards that aren't discarded are returned to the top of their players' Decks.

The Secret History of SpyEdit

In an article on Board Game Geek, Donald X. Vaccarino commented on the development of Spy:

I made this for the 4th expansion during development of the main set, and almost immediately stole it for the main set. It was just too perfect; it's an attack that doesn't feel like the other ones, it interacts with a bunch of things, it's hard to evaluate. It's "free" (it has +1 card, +1 action, so playing it doesn't use up your action and it doesn't take up space in your hand), and those cards are hot tickets.[1]