The interior plan of the church consist of a nave , a short transept , and a semicircular apse . At the west end of the nave is a narthex . At the center of this is a vestibule leading to the church 's main entrance ; at the church 's northwest corner is a reconciliation room , formerly a baptistry ; at the southwest corner is a short passage from which a staircase descend to the basement and another rise to the choir loft . In the loft is the church 's organ , a tracker model manufactured by the Hinners Organ Company in 1879 ; the organ was not originally built for St. Leonard 's .