Some doors should never be opened.

Morgan Ellis, a struggling Chicago real estate agent, desperately needs the sale of apartment 5P at the historic Bellweather Residences to save her sinking career. But during a routine Saturday open house, she makes a horrifying discovery: a dead woman lying on the master bedroom floor, wearing a distinctive vintage cameo brooch. Just ninety seconds later, when Morgan returns with a witness, the body has vanished without a trace.

Dismissed by the police as stressed and delusional, Morgan refuses to let it go. She discovers that the apartment belonged to Vivian Aldiss, a wealthy philanthropist who supposedly died of cancer in Arizona six months earlier. As Morgan delves deeper into the secrets of the 1928 Art Deco tower, she uncovers a forgotten architectural blueprint featuring hidden service corridors and a secret elevator shaft concealed behind the bedroom closet.

Soon, Morgan realizes she wasn't hired by Vivian's charming son, Graham, just to sell the property. She was hand-picked to be the perfect, compromised fall guy in a massive, multi-million-dollar laundering scheme. Trapped in a deadly game of cat and mouse within the walls of The Bellweather, Morgan must navigate the building's dark circulatory system to find out if Vivian is truly dead—and if the person who saved her might actually be the one keeping her prisoner.