Abstract. We describe explicitly the correspondence of Edge between the set of planes contained in the Fermat cubic 4-fold in characteristic 2, and the set of lattice points T of the Leech lattice Λ 24 such that OABT is a regular tetrahedron, where O is the origin of Λ 24 , and A and B are fixed points of Λ 24 such that OAB is a regular triangle of edge length 2. Using this description, we present Conway's isomorphism from PSU(6, 4) to ·222 in terms of matrices.