Complex sentence: The city's patron, Signora Rosanna Calvierri, claims that the Black Plague runs rampant outside of Venice, but the Doctor says this is false and it appears she is using this as an excuse to seal off the city.
Split into simpler sentences: The city's patron, Signora Rosanna Calvierri, claims that the Black Plague runs rampant outside of Venice. The Doctor says this is false and that it appears she is using the plague as an excuse to seal off the city.