The main character of the series is a schoolboy named Arnold, who lives with his grandfather Phil and his grandmother Gertrude in the Sunset Arms boarding house, which they own. His parents Stella and Miles disappeared when they took part in a rescue operation in a distant country. The setting is the fictional town of Hillwood. The plot of the series comprises Arnold's school adventures with his friends and stories involving the residents of the boarding house owned by his family. A special place is given to the tale of Helga's secret love for Arnold, in which she cannot confess her feelings to him, as well as the struggle with her father's emerging business ideas, which in some way threaten the quiet and peaceful existence of the town.