Have an interest in or meddle in something. For example, When they nominated me for the board, I'm sure Bill had a finger in the pie. Another form of this idiom is
have a finger in every pie, meaning “to have an interest in or be involved in everything,” as in She does a great deal for the town; she has a finger in every pie. The precise origin of this metaphor, which presumably alludes either to tasting every pie or being involved in their concoction, has been lost.
[ Late 1500s