If you are having trouble formulating a concise log-line for your story, chances are your plot is suffering from DGD (Dramatic Grammar Deficiency), or - worse - that you are failing to grasp the emotional logic of what is actually going on as evidenced by the actions and interactions of the characters. If this is not the case, then basically what you have to do is, look at the beginning of the second act of your story. That is the main chunk of it. You imply Act 1 with your protagonist’s adjective of manner that contrasts them against the new world of Act 2 they have dived deep into. You also must imply the consequences of the protagonist failing in your log-line to make things not boring when you tell someone about it so they’ll want to know more. That’s literally all there is to it.

1. "If you can't say it in one
sentence, you don't know what
it's about."

2. WHO?
 TELL or SHOW us what kind of person the main
character is. are, which is done most effectively by
conjuring a picture or image of them that in some
way epitomizes their essence or dramatic identity
or the relevant given circumstances that have a
bearing on their choices and actions. For example:
A rock'n'roll arsonist; a troubled young girl; a
rebellious family man; a cynical police detective,
an alcoholic lawyer; and so on.

3. WHAT?
 WHAT is the protagonist’s main
objective in the story? What is it that
they desire, remembering that
dramatic action is goal-directed action.
Do they want to protect their family?
Win someone's love? Discover the
identity of a murderer? Redeem the
sense of their own integrity?

4. WHY?
 Is the action DRAMATIC? In other words, what is at
risk? What are the stakes? The possibility of the death
of a loved one? The destruction of a way of life? A
travesty of justice? The punishment of an innocent
under the guise that they are guilty?

5. EXAMPLE LOGLINES
 West Side Story (based on Romeo and Juliet).
Two young lovers associated with rival gangs in the
slums of New York try to escape the bigotry and
violence that surrounds them to find a better life.

6.  Jaws
A land lubber sheriff tries to kill a giant shark to
protect his family and seaside resort town.

7.  The Verdict
A down-at-heel lawyer seeks to redeem his self-respect
by defending the rights of a young medical-
malpractice victim against the city's leading Catholic-
owned hospital, and city's biggest and most
prestigious law firm.

8. A GREAT LOGLINE WILL
 Reveal the protagonist’s SITUATION
 Describe the ACTION the protagonist takes
 Reveal the important COMPLICATIONS
 Hint at the CLIMAX - the danger, the 'showdown'
 Hint at the protagonist’s potential
TRANSFORMATION
 Identify SIZZLE: sex, greed, humor, danger, thrills,
satisfaction
 Identify GENRE

9. PRESENT TENSE, PLEASE!
 Keep it in present tense, and pack as much potent
visually dramatic information as you can without
losing the edge and attitude of the story.

10. In conclusion
 Remember - a screen story's log-line should tell the
reader who must do what in order to prevent what
from happening.