Dina, a tenacious art forgery expert (This is confusing, is she an expert at forging art or is she an expert at detecting forgeries? it can be read both ways), is suddenly (Don’t need to say suddenly) dragged back into her past life (Past life as a what?) when an extraordinary package (What specifically makes this package extraordinary a package full of talking bees? That would be extraordinary) is left at her apartment by a mysterious man who seems to know the most personal and intimate details about her past. (Still haven?t told us about her past)

Why now? (Not needed) Can he be trusted?(Not needed) With new revelations (Of what?), her life quickly spirals into a maelstrom of confusion (Not needed) and Dina is torn between her innocent desire to believe the stranger (Still haven’t told us what the revelation is, if you tell us the revelation, we might understand why she wants to believe) and her professional instincts telling her that everything is not as it seems. (You should cut everything after the word instincts)

As she struggles to understand what is happening, (Not needed) an unsolved, decades-old crime (What crime? murder? kidnapping? be specific) linked to a missing treasure (Missing diamonds? Missing paintings by Rembrandt? be specific) becomes the center of her life.

Embarking on an unexpected and mystifying adventure that interrupts her busy life (Not needed), Dina must confront the shadows of her past (How will confronting shadows of her past help solve the mystery) and face the truth about her family.

What happened more than twenty years ago when her father and brother were torn away from her? (Not needed) Together with her colleagues (Be more specific, a dance teacher and and ex-rugby player for instance) and their expertise, the mystery might be solved. But will her team unconditionally support her in her effort to put together the pieces of this long-broken puzzle? (Not needed, basically if your sentence ends in a question mark, it should be deleted)

To shed light upon the truth, Dina will have to travel to a place (A place? be specific Peru, Berlin, Disneyland) that holds many painful memories (Of what?) and face the ghosts of her past (Redundant, you already said she must confront shadows of the past).

There she will learn about the fate of her doting father and beloved brother, (Doting and beloved are not needed) who has (have) been lost to a shadowy, clandestine (Saying both shadowy and clandestine is redundant) organization known only to a few locals (Since you haven’t told us where we are, you don’t need to say ‘to a few locals’) as Corridor One.

Dina will have to rely on the help of an unlikely partner (An old gypsy? a grizzled veteran? Be specific. Unlikely partner is too vague) and an old, long-forgotten (If it’s long forgotten how can she rely on it) Siberian mental art to accomplish her goals. But is Dina alone on her path or is somebody quietly watching her steps? (not needed)
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One thing I have noticed, in both the logline and your synopsis, there is no clue as to how the lead character’s being an ‘art forgery expert’ connects to the story, nor have you told us what her past life was so we don’t know how that connects to the story either.

Who she is and what the adventure is, should connect to one another and should be represented in your description of the story.

For instance, if the ‘treasure’ has to do with forged art then we could see how it would all connect, but since you only say ‘treasure’ but don’t give us any details as to what that treasure is, we are lost as to how it all connects.
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Hope this helps, good luck with this!