Complex sentence: Windrush is finally posted to train as a Japanese interpreter, where he becomes the prize pupil; he's then contacted by his uncle, now a senior officer in the War Office, to join a secret operation known only as "Hatrack".
Split into simpler sentences: Windrush is finally posted to train as a Japanese interpreter, where he becomes the prize pupil. He's then contacted by his uncle, now a senior officer in the War Office, to join a secret operation known only as "Hatrack".