A young woman named Izzy Ames is in a committed and loving relationship with Cyrus Rivera, her high school sweetheart. Together, the two live near the Salton sea in California in the United States. At first glance, they are a seemingly picture-perfect couple. They are both attractive. They are both intelligent. And perhaps most importantly, they are both committed to each other.
However, they both are dealing with significant traumas that have occurred in their lives. But they are each other's rocks and support systems. Without each other, it seems, they will fall apart mentally and physically. They lead a reasonably sheltered life but are friends with a couple named Nephy and Seth, who they quickly bond with.
One day, Izzy wakes up to find Cyrus gone. He didn't leave a note and Izzy can't seem to find him anywhere. She looks everywhere she can for him, but isn't able to find him—even with a bit of help initially. However, eventually, Izzy realizes that no one is truly willing to help her find Cyrus. Thus, she decides to search for Cyrus by herself. She spends weeks looking for Cyrus to no avail. She can't even find a clue as to where Cyrus is. Discouraged but not defeated, Izzy perseveres and continues to look for him.
Eventually, she discovers a clue that leads to the eponymous House of Hearts, which is a retreat center run by an enigmatic woman named Sky. Izzy embeds herself in the House of Hearts and starts to meet several people, including a young woman named Ever Fontana. Izzy and Ever grow close and Izzy can overcome her trauma and her grief.
While at the House of Hearts, Izzy discovers a lot about herself and a lot about the retreat center, which she quickly discovers has more going on than it seems. She discovers that the House of Hearts is a depressing and dark place filled with desperate people. Ultimately, she finds Cyrus but learns quite a bit about herself along the way.
