A logline’s purpose is not solely the brief summation of a movie. The real intention of a logline is to hook your audience (whether that audience is an agent, executive, producer, actor, or box-office patron). A logline needs to grab your audience’s attention through dynamic wording and engaging ideas. It needs to accurately capture the movie’s narrative while also pithily including language that will emotionally involve the listener.
The highwire act to walk here is to reveal the premise of the movie while not revealing too much of the plot. The key is creating a mystery or question your audience wants to know more about. And of equal importance is keeping the logline short and snappy. To boil it down, in essence, a logline’s chief purpose is to say much while using very little.