Pat Flanngan, an American with Irsh ancestry, was a U.S. Navy aviator who appeared in Biggles in Borneo. He was the rear gunner in a U.S. Navy aircraft stationed or operating in the Philippines. Out on a reconnaissance flight with his pilot Bill Gray, they had been shot down, taken prisoner, and sent to the Cotabato prison camp where they had met Jackson, a British diplomat who had also been captured. Gray and Flanngan attempted to escape but had been recaptured. As they had struck a Japanese soldier during their escape attempt, General Yashnowada, the brutal commander of the prison camp, had sentenced them to be flogged. The punishment, however, only strengthened their determination to escape again and they made a second attempt together with Jackson, which succeeded.

Gray, Flannagan and Jackson stole a sailibng boat and attempted to reach Australia. However, when sailing down the coast of British North Borneo, they were discovered and pursued by a Japanese patrol boat. Fortunately the Japanese boat was spotted and sunk by Biggles and the others on their first patrol out of Lucky Strike.

Short of food and water, the trio had turned inland, proceeding upriver in their boat but Japanese troopsin canoes continued to pursue them, guided by a Kawanishi E7K seaplane. Forty miles from Lucky Strike, their plight was spotted by Punan warriors in the jungle and the news transmitted to Lucky Stirke. Ginger suggested packing a survival kit with food and medicines to be dropped to them. Biggles agreed and took Ginger up in a Beaufighter while Captain Rex Larrymore and Suba led a rescue party to try to reach them overland. The Beaufighter found Gray's boat under attack from the Kawanishi seaplane and promtply shot it down. Ginger then parachuted down with the supplies, meeting Jackson, Gray and Flannagan, who had come ashore after their boat had been sunk by the seaplane.

By the next morning, the Japanese pursuers had almost reached the Ginger and survivors but were destroyed by Suba's warriors and the Beaufighters just in time. Gray and the others were then carried to Lucky Strike by the Punans, an overland trip through the jungle taking two days.

Together with Gray and Jackson, Pat decided to remain behind at Lucky Strike to help out instead of being evacuated to Australia. His role in subsequent events is not described in the book, but it is likely that he took part in Biggles' rescue mission to Cotabato. As an aviator who knew the target area well, and with 666 Squadron shorthanded, it would have been extremely unlikely for him to have been left behind. Most likely he would have manned one of the gunner positions on the Beaufighters or the Liberator.

At the end of the book, Flannagan departed Lucky Strike on board a Liberator together with Biggles, Jackson, Bill Gray and the rest for a well-earned rest in Australia.