Complex sentence: Not long after, Pup has already decided he must rescue his brothers and sisters, and he pleads with Octo to build him a machine which would allow him to travel on land, but Octo refuses to do so.
Split into simpler sentences: Not long after, Pup decides that he must rescue his brothers and sisters. He pleads with Octo to build him a machine which would allow him to travel on land, but Octo refuses to do so.