Gruesome copycat murders hit a sleepy-coastal town, forcing an excited rookie to seek the help of a miserable retired detective, only to stumble upon information that endangers both their lives.
Who is the main character, the protagonist? The rookie or the retired detective?
Also it’s better to frame a character’s actions in terms that describe him as proactive, as acting on his own agency. So the situation doesn’t “force” the rookie; rather the situation triggers him to consider choices. The choice he makes of his own volition is to consult the detective.
Also when does the discovery of the new information occur? If it occurs after the plot has already been set in motion, if it’s a discovery/reversal at the midpoint than it probably does not need to be in a logline. For one thing, it’s expected that murder mysteries will entail a Shocking Discovery and that the life of the protagonist and/or a stake character is in danger. For another, I don’t think it increases interest in reading the script by playing hide and seek with the discovery, by not disclosing what makes this discovery so different, so unique from the other discoveries in other murder mysteries.
On the other hand if the Shocking Discovery occurs at the end of Act 1 and pivots the story in a whole new direction, then what that discovery is needs to be revealed in the logline. (Example: The Shocking Discovery of the body of the Evelyn Mulwray’s husband in the reservoir in “Chinatown” at the and of Act 1 pivots the story in a new direction, triggers private eye Gittes to pursue a whole new objective goal.)
Whatever. My point is that the only element of information a logline that should never give away is how it ends. Other than that, every element should inform, not obscure, should be specific, not vague.
“When gruesome copycat murders hit a sleepy coastal-town, a rookie cop enlists the help of a retired detective to hunt the killer.”
Agree with other comment that discovery of info probably doesn’t need to be here. Their lives are going to be in danger bc they are hunting a killer after all. I’m guessing that since you put “copycat” in there and this vague “information”, they are going to find out that somehow another cop was involved in original murders and maybe current ones. Which has been done many times before. But I could be wrong! And even if I’m right, a brilliant script is a brilliant script even if has similar plot to others.