p.boxed
  | One of the pawns of each side is a disguised queen.
  | She is revealed only when not moving like a pawn.

p.
  The hidden queen cannot give check (because the opponent cannot see her
  nature), but she could sometimes capture the king. This capture ends the
  game. Except that, everything goes as in orthodox chess.

figure.diagram-container
  .diagram
    | fen:rnbqkbnr/ppp1tppp/8/3P4/8/8/TPPP1PPP/RNBQKBNR:
  figcaption After 1.e4 d5 2.exd5

p.
  In the diagram position, if the black hidden queen is on e7 then
  they can play 2...Qxe1, revealing her identity and winning at the same time.

h3 Source

p
  a(href="https://dames-cachees.herokuapp.com/rules") This website
  |  developed by Etienne Orieux (2019)
  | introduces the rules and allow to play in live,
  | with a deterministic initial position but a user-defined
  | location of the hiden queen.