RE: When a young detective gets challenged by a killer, he will have to ask help to his wise mentor with whom he had fought hard.
Young is rarely a good description for a main character, but I get where you’re coming from in your logline: the detective is inexperienced and thus has to find help by asking his mentor.
But better if you go with inexperienced or half-baked. That’s a more visual description and states his flaw in a clearer way.
Also: replace challenged with something more urgent. Maybe they kidnap someone close to the detective or someone else, just give the character a clear visual goal he has to take on as an active part of the story. Right now, he is just asking his mentor for help. But it’s your main character (detective) we want to see achieve the goal of your story.