The Last Open House. The Bellweather Residences, #7

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.