Related Clues:
- Known to but a few
- Understood only by a few
- Doctor erects what should be know to few
- Erects building out of the way
- Mysterious or understood by few
- An acre (anag)
- Apprehended by a small group
- Not public school receiving royal backing
- Dark forces clued around this grid
- Like much tax law
- Woody, Arlo or Gwen maybe
- One not to be divulged
- Something hidden from E. Phillips Oppenheim and Laurence Binyon
- Not known by others
- Security classification level