Insidious Sevens is a trick-taking game in which players predict how many tricks they will win each round. The deck consists of 40 cards, numbered 0-7 in five colors, with the colors ranked on the cards: purple (high), blue, green, yellow, red (low). Note that all 7s are higher than any 6, which are each higher than any 5, and so on.

At the start of a round, each player is dealt seven cards. Players pass 0-3 cards to their left or right neighbor depending on the round number. Players then predict the number of tricks they'll take by choosing a card in their hand and simultaneously revealing them. The player with the highest bid becomes start player for the round, and the color of that player's card indicates the trump suit for that round. These bidding cards are then returned to the players' hands.

The start player for a trick lays down a card, and each player must follow the lead by playing a card of the same color or number. If this isn't possible, they can play any card. The highest trump card played (if any) wins the trick; otherwise the highest card played that followed the lead (including number!) wins the trick. After seven tricks, the round ends. Making one's bid nets two points plus the number of tricks bid, while missing results in a loss of one point for every under- or over-trick. The player with the highest score after seven rounds wins.

An optional rule forbids the bids from summing to seven. If this occurs, the player with the highest bid scores one point, then the bid cards are set aside and players rebid from the cards remaining in hand. This process can repeat until the total of bids made does not equal seven.