The TARDIS arrives in London in 1966 and the First Doctor and Dodo visit the Post Office Tower. There they meet Professor Brett, whose revolutionary new computer WOTAN (Will Operating Thought ANalogue) can actually think for itself and is shortly to be linked up to other major computers around the world — a project overseen by civil servant Sir Charles Summer.
| Writing | Kit Pedler | Idea |
| Writing | Ian Stuart Black | Writer |
| Directing | Michael Ferguson | Director |
| Production | Innes Lloyd | Producer |
| Writing | Gerry Davis | Script Editor |
