Simon lived among the ruins of London during the 22nd century Dalek invasion. For several months, he was kept safe by utilising the Doctor's TARDIS. He lived inside the demarcated "danger zone" and, one day, found himself pursued by wolves while on an excursion to find food. In his flight, he dropped the tin of baked beans he had found and ran into the TARDIS.
He put his hands on the console and pleaded for help. The Twelfth Doctor and Clara Oswald materialised near him. The Doctor explained that he must have used the telepathic circuits and had materialised the craft around him and Clara. He then took Simon to Bedfordshire where he was reunited with his mum and dad. (PROSE: When the Wolves Came)