The game is described in Murray's history of chess, Gollons book, Pritchard's Encyclopedia of Chess Variants, and some other books on the history of chess. Gollon mentions this variant as 'considered especially interesting by the author', i.e., by himself.
Players have twenty-four pieces: twelve pawns, a king, a man (counsellor), a queen, a schleich (spy or smuggler, also translated as fool), two couriers, two bishops, two knights and two rooks.
King f1; Queen g1; Rook a1, l1; Knight b1, k1; Bishop c1, j1; Courier d1, i1; Man e1; Schleich h1; Pawn a2, b2, c2, d2, e2, f2, g2, h2, i2, j2, k2, l2.
King f8; Queen g8; Rook a8, l8; Knight b8, k8; Bishop c8, j8; Courier d8, i8; Man e8; Schleich h8; Pawn a7, b7, c7, d7, e7, f7, g7, h7, i7, j7, k7, l7.
The game starts with moving three pawns and the queen in a particular way, such that the following position arrives:
King f1; Queen g3; Rook a1, l1; Knight b1, k1; Bishop c1, j1; Courier d1, i1; Man e1; Schleich h1; Pawn a4, b2, c2, d2, e2, f2, g4, h2, i2, j2, k2, l4.
King f8; Queen g6; Rook a8, l8; Knight b8, k8; Bishop c8, j8; Courier d8, i8; Man e8; Schleich h8; Pawn a5, b7, c7, d7, e7, f7, g5, h7, i7, j7, k7, l5.
With this position, the game really begins.
The courier moves as the modern bishop.
The bishop (in courier chess) jumps two squares diagonally, so like the elephant in Shatranj (which undoubtly also is the origin of this type of move.)
The queen moves one square diagonally.
The man moves one square in an arbitrary direction, so like the king (but without being hindered by check etc.)
The schleich moves one square horizontally or vertically.
Pawns move as pawns in orthodox chess, but cannot make a double move from the second row. The promotion rule for this game is not known, but most likely, the rule is that a pawn promotes to queen (with the movement of a queen in courier chess) when arriving at the last rank.