Tony Stark is a brilliant, sarcastic, and stubborn genius who relies on technology and logic. After the Project HOLLOW incident, he investigates the impossible security footage appearing throughout Avengers Tower. When recordings reveal a double wearing his face, Tony becomes determined to uncover a scientific explanation, even as his own security systems begin behaving strangely. For the first time, he faces something he cannot easily explain or control.

Steve Rogers is a courageous, disciplined, and compassionate leader who prioritizes his team's safety. As supernatural incidents escalate, he establishes rules to protect the Avengers from being replaced by impostors. However, hearing his own voice coming from empty rooms forces him to question what is real. Despite growing paranoia, Steve struggles to keep the team united as suspicion threatens to destroy their trust in one another.

Natasha Romanoff is an observant, calculating, and highly skilled spy who rarely reveals her emotions. She investigates corrupted surveillance footage and discovers recordings of impossible hallways filled with motionless figures. Suspicious of everyone, including herself, Natasha searches for inconsistencies that could expose the impostors. However, the entity begins mimicking even the smallest details of human behavior, making it increasingly difficult for her to distinguish truth from deception.

Bruce Banner is an intelligent, soft-spoken scientist who prefers rational explanations. He studies the biological anomalies connected to Project HOLLOW, discovering evidence that the entity can imitate human behavior without possessing a normal biological structure. As his research becomes increasingly disturbing, Bruce fears that the creature may eventually learn to imitate even the Hulk. Meanwhile, the stress of the haunting threatens his already fragile sense of control.

Thor is a powerful Asgardian warrior who is courageous, loyal, and protective of his companions. Despite his experience with ancient magic and terrifying creatures, he cannot identify the presence haunting Avengers Tower. He senses something older and stranger than any ordinary supernatural being. His attempts to confront it with divine power produce unsettling consequences, forcing Thor to consider that this enemy may not follow the laws of gods or mortals.

Clint Barton is a resourceful, sharp-eyed marksman with dry humor and strong instincts. He helps secure Avengers Tower and watches for suspicious movements when technology becomes unreliable. However, he begins hearing his family's voices through the communication systems, despite knowing they are nowhere nearby. The experience unsettles him more than he admits, making him increasingly determined to protect his teammates from whatever is manipulating their minds.

Nick Fury is a strategic, secretive, and highly experienced leader who trusts evidence more than assumptions. As the former director of S.H.I.E.L.D., he investigates the classified Project HOLLOW incident and the disturbing events unfolding inside Avengers Tower. Fury knows the project concealed information even from high-ranking officials, but the surviving records offer more questions than answers. As the Avengers begin doubting one another, he warns them that the entity may be deliberately manipulating their trust. However, Fury keeps certain details about Project HOLLOW to himself, raising the unsettling possibility that he knows more about the entity than he admits.

F.R.I.D.A.Y. is Tony Stark's advanced artificial intelligence, responsible for monitoring Avengers Tower, managing security, and assisting the team. After Project HOLLOW, she begins detecting additional occupants, recording voices belonging to absent teammates, and displaying security footage that contradicts reality. Tony suspects her systems have been compromised, but F.R.I.D.A.Y. cannot identify the source. The most disturbing possibility is that something has learned to communicate through her, leaving the entire Tower's security unreliable.