Complex sentence: In September 1942, Hodder & Stoughton published Blyton's first Famous Five novel, "Five on a Treasure Island", a series that became tremendously successful and resulted in the writing of 21 books between then and 1963.
Split into simpler sentences: In September 1942, Hodder & Stoughton published Blyton's first Famous Five novel, "Five on a Treasure Island". The series became tremendously successful and resulted in the writing of 21 books between then and 1963.