Complex sentence: The plan requires them to pass through the cage where the Teller is kept in hibernation; the Doctor realises that because the Teller can sense guilt, they had undergone the memory wipe to minimize the chance of them being detected.
Split into simpler sentences: The plan requires them to pass through the cage where the Teller is kept in hibernation. The Doctor realises that because the Teller can sense guilt, they had undergone the memory wipe to minimize the chances of their being detected.