Terminally ill single dad romances a vulnerable heiress to procure a new home for his son, but his unexpected connection to her past jeopardizes his son’s life and thrusts fates of others into his hands, just as the time runs short.

Slight revision:

A terminally ill single father romances a vulnerable heiress to?secure a home and future for his son.

"Terminally ill" implies the inciting incident that motivates his action -- what he is incited to do as a result of the diagnosis.

Your logline tells the story from the point of view of the father, which is okay.? But for your consideration, I think there is ?an even more interesting story line?embedded in the concept, that of the son. Who, after all, is the stakeholder, the one who has to live with the consequences of his father's action.? What if the heiress likes him? -- but he doesn't like her?? What if, instead, he prefers his real mother, a woman of modest means who?cannot provide him with the material support and future opportunities that the heiress is all to eager to shower upon him?

What if he likes his ?step-mother and certainly likes? her lifestyle, but the heiress does not like him?but accepts him as part of the "package deal"?? Only to?reject him when the truth comes out about his terminal illness-- as it surely will -- and?she realizes she's ?been conned by his father?

I don't know where you're going with the concept, but I can see many interesting possibilities.? Good luck with your writing.

The core of the story, the hook, is ?the terminally ill father wooing the vulnerable heiress to provide for his son after he's dead. ?And it's a good one.

The rest of the logline is confusing, vague. ?I have no clear sense of what or how the past jeopardizes his effort. And in a logline the threat or obstacle to the main character's goal needs to be clearly defined; a logline reader is entitled to know -- needs to know -- exactly who/what threatens to defeat the protagonist.

I presume the father is not revealing his illness to the heiress -- a willful act of deception that will jeopardize their relationship, his objective goal, when the truth comes out. ?As it surely will. ?I also presume the son is initially in on the "con".

IOW: ?I think there is enough inherent potential for complications, conflicts, dramatic tension and suspense in your core concept without having to clutter up the story with yada-yada about dark secrets and the fate of others.

I suggest focusing the logline (and the plot) on the core of the story. ?In this case, I think?less? is more.? I like the hook. A lot. It invokes a lot of possibilities in my mind.? Trust the conflicting emotions that flow from the? setup.? Best wishes.