I am not a legal expert, and NZ does not maintain the distinction between the two that the British system does, but I think that solicitors handle much of the business of law. E.g. they draw up wills and contracts, provide legal opinions and the like. A barrister confines themselves to arguing in courts. So as a solicitor would have helped Sir Walter draw up the rental contract with Admiral Croft, but if it was disputed and got to the courts he would brief a barrister to argue the case in the court.