Billy Bishop Goes to War is a unique play and the simplicity of it lends itself to Bishop's own real life character. Billy tells his story to the audience as if they are his friends, making the setting of a bar - with a piano player, of course - all the more relevant. Billy basically re-lives the events and takes on various characters(and voices) as he explains to his "friends" - the audience - what they said to him. He looks to the piano player regularly to reinforce what he says, sometimes repeating himself so as to get confirmation and agreement.
The piano player is the narrator when Bishop is not speaking, singing and playing the piano in the background throughout with the odd sound effect, changing the tempo to suit the particular stage in Bishop's story. Sometimes he sits and listens intently and other times encourages Bishop to join him in singing as if they had been in battle together and their story is shared.
Although the piano player does not necessarily actively engage the audience, he does connect with them as if they are there to listen to him - the entertainment for the evening- as well as Bishop's story.