Crosbie was the first son of Norman GARSTIN and his wife Dochie, and the older brother of Denis (d 1918 at Archangel) and Alethea GARSTIN who grew up in the artist colonies of West Cornwall. He proved to be a creative force in several artistic directions. Not a good pupil, he was nevertheless an excellent athlete, becoming head boy at his school due to his captaincy at rugger and swimming.

In the summers he accompanied his parents on their summer schools abroad, making friends and colleagues with many artists such as Frances HODGKINS and other pupils working under his father's tutelage. From 1912 he went abroad to 'the Dominions' to make his living as a cowboy, a sailor, a jack of many talents, but returned from Africa when war was declared, and joined up (King Edward's Light Horse).

He also studied briefly at the FORBES SCHOOL [Ed: Hale comments there is no evidence for this], but like his friend, Fryn JESSE, he turned his talents to writing. His first book Vagabond Verses, for which Alethea designed the cover, was published in 1917.

He is best known as a novelist, creating the Penhale trilogy: Owls' House (1923), High Noon (1925), and The West Wind (1926), and collaborating with Mrs Alfred Sidgwick on the novel The Black Knight. He was also the writer of the poem 'Rondeau' better known as 'On Newlyn Hill' as set to music for a Cornish male voice choir.

His unexpected disappearance in 1930, surmised to be in a boating accident (no trace or body ever found) is one of West Cornwall's enduring mysteries.