Complex sentence: Continuing from "Dark Water", Clara Oswald is trapped with a Cyberman in the headquarters of 3W in St. Paul's Cathedral, and when it tries to' delete' her due to her irrelevance, she uses her knowledge to claim she is the Doctor.
Split into simpler sentences: Continuing from "Dark Water", Clara Oswald is trapped with a Cyberman in the headquarters of 3W in St. Paul's Cathedral. As it tries to' delete' her due to her irrelevance, she manages to stop its attack by stating she is, in reality, the Doctor.