Doom placed normally on the agenda are all "in play", not just those littered on enemies and locations. (rule)

In Play and Out of Play

The cards that a player controls in his or her play area are considered in play.

The current act, the current agenda, each location in the play area, and each encounter card in a investigator's threat area or at a location, are all considered in play.

Out of play refers to the cards in a player's hand, in any deck, in any discard pile, in the victory display, and those that have been set aside and/or removed from the game.

A card enters play when it transitions from an out-of-play origin to an in play area. A card leaves play when it transitions from a in play area to an out-of-play destination. Tokens on in play cards are considered in play. Resources in each investigator's resource pool are also considered in play.