Aloysius Pendergast owns the Beaux Arts mansion at 891 Riverside Drive, between 137th and 138th streets. From the outside, the mansion appears to be well-maintained but unoccupied, an appearance carefully preserved by its current and former owner, both of whom value privacy.
The mansion was originally owned by Pendergast's great-great-uncle Antoine Leng Pendergast, alias Enoch Leng. Leng acquired the mansion, originally an abbey, in the late 19th century after he was expelled from the Pendergast family in Louisiana.
Leng experimented with chemical substances meant to prolong his life. He succeeded in doing so by extracting a compound from human spinal columns. Leng killed many people to obtain the necessary chemicals and lived into the late 20th century. He stopped taking the compound in 1954 but was still alive until 2002, when he was killed by Anthony Fairhaven, a property developer who is similarly obsessed with eternal life and tracked Leng down to the mansion.
The Riverside Drive mansion contained Leng's cabinet of curiosities, a collection of artifacts and natural substances including toxic plants and insects that he collected over his long life. The cabinet of curiosities also included Constance Greene, a young girl who Leng kidnapped in the late 19th century and kept eternally young using his compound. After Leng's death Aloysius Pendergast discovered her in the mansion and adopted her as his ward.
Riverside Drive now serves as one of Pendergast's bases of operations in New York City and is Constance's primary residence when she is in New York.
The mansion contains a smuggler's tunnel leading to a hidden boat dock on the Hudson River. Aloysius Pendergast believed that the tunnel entrance was undiscoverable, but his son Alban used the tunnel to enter the house and kidnap his twin brother Tristram.