I tried to create a ground-zero event, but it was obviously only there to be 'the incident'. Then I tried to scrap the story in the past and bring its event forward. Ruined everything - not enough time had passed. Finally I examined the motivations of the hero and heroine. To my intense relief, the tangle started to undo itself. It was clear that each of them had to have their own reason for getting involved in the story.
So in the present, there are two inciting incidents for the action plot. Additionally, there must be an inciting incident for the romantic plot. That makes four plot lines, when I had made myself believe that there would be only two - one each for the past and present. How I could do that when the single-timeline story I just finished had dual plot lines - one each for the action and romantic plots - is a mystery. But for now at least, I am no longer imitating a pretzel.