Yours: “An ex-marine turned assassin reconsiders his occupation when he finds out he has a sister: A detective that’s hot on his trail.”

– Which comes first: discovery he has a sister or learning there’s a cop hot on his trail?

– dpg pointed out the problem with your LL. “What’s this movie about?” “It’s about an assassin reconsidering his occupation.” “Thank you. NEXT!” 🙂

– We don’t need the info about him being an ex-marine. It doesn’t matter — not as is. The story through-line is him learning he’s got a cop hot on his heels, the kicker being she’s his sister.

How about:

“An assassin goes to war with the detective hot on his trail, then discovers she’s his long-lost sister.”

Let’s rerun the “What’s this movie about?” test: “It’s about an assassin who goes to war with the detective hot on his trail.” “Okay, tell me more…”

– So, this raises many questions about why the family bond matters and what happens AFTER the familial discovery. That seems to be the real story here. The familial reveal feels to me like an Act One turning point, because it’s the thing that generates the most conflict, the hardest decisions. The revised LL as it stands can’t describe a full story arc, because if the reveal comes at the end then we’ve just vented any intrigue our LL had. Using the elements you provided I can picture a story shaping up like this:

“An assassin finds out the detective hot on his trail is his long-lost sister. To avoid a lethal showdown they agree to work together to hunt down his ex-marines cop-killing boss.”

Boom: trigger, protag, antag, situation, motivations, stakes, probably a ticking clock or two. All from turning “reconsiders his occupation” into a clear, tense goal.