In Biggles in the Blue, Commander Evans was a retired Royal Navy officer who was the neighbour of ex-Nazi Werner Wolff who had been hiding in Jamaica at a villa named Rumkeg Haven under the assumed name Christen Hagen.
During Wolff's stay in Jamaica, Evans made a brief acquaintance with him. Evans was an amateur ornithologist and hoped to write a bird about West Indian birds. Wolff had offered to help him with his hobby by getting him some photos of the scarlet flamingo and collecting one of their eggs for his private museum while out on his occasional cruises on his yacht.
After Wolff's death, Biggles called on Evans. Evans told him about his acquaintance with Wolff but also mentioned that a foreigner (von Stalhein as it turned out) had seen him under the guise of an insurance investigator, asking the same questions. Biggles told Evans that in fact already collected a flamingo egg for him and it was lying in Wolff's sitting room. Evans, highly excited to hear of this, asked if he could have the egg. Biggles then suggested leaving Wolff's house keys with Evans so that he could fetch the egg at his convenience, and also have the keys on hand in case Biggles or his colleagues should need to return to Rumkeg Haven again.
Just as Biggles and Ginger were leaving, they hear a scream coming from Rumkeg Haven and rush to investigate. It turned out to be Evans--apparently he couldn't wait for the egg and had decided to collect it immediately. While in Wolff's house he had been bitten by a snake planted by Napoleon Morgan, a Trinidadian gangster working for von Stalhein and Zorotov. Quick action by Biggles removed most of the venom and Evans was safely transported to a hospital.
Later, Ginger and Bertie called on Evans in the hospital to ask him if he knew where Wolff would normally develop his photographs, hoping that a view of his photos might yield a clue as to where Wolff had been in his yacht. Evans was able to direct them to Johnston, a chemist whom he had recommended to Wolff.
At the end of the book, Ginger fetched another flamingo egg from Inagua for Evans, an act which, he hoped, would complete Evan's recovery.