Use 'but then' to show an unexpected or surprising change in the situation.

Surprising Turn

'But then' can be used to contrast ideas, suggesting a rethink or second thought.

Contrasting Ideas

It often signals a change in the speaker's opinion or decision.

'But then' links actions chronologically, with the second action following the first.

It can imply a cause-effect relationship between two events in time.

In storytelling, 'but then' often sets up a surprising or dramatic twist.