How does Donald continue to help Bertha after he is stationed in San Francisco?

Donald Lam joined the Navy at the outbreak of war between Japan and the United States. The brains of the team, he helps Cool with telegrams from San Francisco, where he is based. It is he who arrives on leave in Los Angeles and solves the murder mysteries and reveals who is really who behind the characters' disguises. Without him, neither Cool nor the plodding police would have figured out the solutions to the novel's various crimes.