The 4th installment in the dominion series. Players must balance their money with the new potion treasure card to buy new cards that help them manipulate their deck and create powerful action chains. Alchemy is a "small expansion", adding only 12 new kingdom cards as well as the Potion treasure.
The Dominion rules are extraordinarily comprehensive. For questions regarding how cards interact, if you can, check the individual card entries in the appropriate rulebook(s) and you'll probably find your answer there. A PDF of the Dominion: Alchemy rules is available here.