rule 4.0 A.2:
Exception: When a player has one card left, he may announce that
he will pass and hold his card. The held card, if applicable, may
be played as an Event during an enemy Action Phase [5.5.6] or
held until the following season. If held until the following season,
the player must play ALL his cards that season. (Place a “Card
Held” marker on the Year track as a reminder.) ~ A player’s held
card counts against next turn’s hand size.
you can hold a card until the next season.
if you hold a card in a late season-turn you may keep it for the following early-season turn.