More from the A to Z of London. The guiding equivalent of a high-wire act. It’s a virtual tour series – three letters per episode – devised and presented by the Fab Five, guides Karen, Adam, Fiona, Russell and Simon. Tonight’s episode – April 25th – was was the turn of the letters S, T and U. Russell and Karen did the honours. Russell took S & T, Karen’s letter was U. Each letter gets three or four “incarnations.” Karen’s selections for the letter U were UCL, umbrellas, the Underground and unicorns. This excerpt was her treatment of the last of those four – London’s unicorns.