Green's new novel is We Hear Voices.
At CrimeReads she tagged seven titles featuring characters with imaginary friends, including:
Memoirs of an Imaginary Friend by Matthew DicksRead about another entry on the list.
The child at the centre of this story, Max, is also eight, and also a loner. In this world imaginary friends have the appearance and powers that the children (or in one case here, an adult) imagined for them. So Budo, our narrator, is pleased to look almost like a regular human, and thanks to his creator Max Delaney, has the power to go through doors (but not walls) and to head off to other places when Max doesn’t need him. Budo is devoted to Max, who is neurodivergent, and when Max vanishes at a time when Budo isn’t with him, has to turn detective and ultimately face a choice between confronting his own greatest fear, and saving his human.
--Marshal Zeringue