Christel Doctor Who of the Week - The Guardians of Time

Although the white guardian of time told the Doctor at the end of Series 1 that they would meet twice more he did not imply how or when. The Doctor also made mention of the other guardians, and seemed surprised by the fact that the white guardian was working alone. The guardian also implied that the Doctor was being tested, and that the 'Choice of ages' was the first part of this test. It is still unknown as to when the next part of the test will be, as well as how or why the guardians are testing the doctor.