Theory:Doctor Who television discontinuity and plot holes/New Earth


 * Why, after locking the Doctor in a door to be injected with diseases, does Cassandra open the same door a few seconds later to let him out?
 * She wanted the contaminated "patients" out and forgot about the doctor for a second.


 * All of the Sisters' cures are intravenous solutions, yet the Doctor is able to cure everyone just by adding them to the disinfectant in the elevator. It is unlikely that an IV solution could be administered topically like that and be effective.
 * The Doctor added lots of other chemicals to the disinfectant, and the disinfectant was from the far future so it would be much more powerful than the 21st century type.