Led by the astute Rex Powell, The Shadowers, Inc. comprises six specialists, each with a checkered past and unparalleled expertise in their respective fields. ​ When the wealthy and influential de Puyster Monckton is found murdered in his historic mansion, suspicion falls on his estranged son, Richard Monckton, who stands to inherit a vast fortune.

As the police build a seemingly airtight case against Richard, The Shadowers are enlisted to uncover the truth. Clifford Nichols, the agency's handwriting expert, takes charge of the investigation, determined to prove Richard's innocence. ​ With the help of the resourceful and intuitive Ethel Jepson, Cliff delves into a world of hidden motives, secret messages, and dangerous adversaries.

From the opulent halls of Monckton Manor to the shadowy underworld of New York City, the team faces numerous challenges, including a cunning jewel thief, a mysterious private detective, and a network of criminals with everything to lose. As the clock ticks down to Richard's indictment, The Shadowers must piece together the clues left in the handwriting on the wall to reveal the true killer and save an innocent man from a grim fate.