Grandpa's Great Escape by David Walliams. Ages 7+.
Grandpa's Great Escape (2015) is a comedy about Jack, whose grandfather — a former RAF Spitfire pilot — is developing dementia. Grandpa believes he is still fighting in World War Two, and his vivid, confused adventures in the present day are both funny and genuinely touching. When the horrible Miss Swine — who runs a terrible care home called Twilight Towers — gets her hands on Grandpa, Jack must mount a daring rescue mission.
The novel handles a difficult subject — dementia in an elderly parent — with great warmth and no sentimentality. Jack's love for his grandfather, and his determination to keep him home and cared for properly, is the emotional core of the story. The flying sequences (in Grandpa's imagination) are joyful.