The two novels are set in his Siren Stone universe, which began with his short story "The Siren Stone", published in Julie Czerneda's anthology Space, Inc. in 2003. In this universe, telepathic asteroids and rocks tap into human minds and make people see the ghosts of their deceased friends and relatives. Both novels also deal with the relationship between science and religion.
In The Moon Under Her Feet, Jesus -- or something claiming to be him -- returns as a teenaged girl to start a nuclear war on the Moon and Earth. In The Shrine of the Siren Stone, a android maid in Tokyo falls in love with an young naval officer just as Japan goes to war for the first time in a century. The two novels are related, but you can read them in any order.