Usage patterns
〈事〉が大詰めに入るfor something to enter its final stage
The negotiations have finally entered their final stage.
〈事〉が大詰めにさしかかるfor something to approach its climax/final stage
The story is approaching its climax.
〈事〉の大詰めthe final stage/climax of something
A dramatic reversal occurred in the final stage of this game.