  A Margulis spacetime is a complete flat Lorentzian 3-manifold M with free
fundamental group. Associated to M is a noncompact complete hyperbolic surface
S homotopy-equivalent to M. The purpose of this paper is to classify Margulis
spacetimes when S is homeomorphic to a one-holed torus. We show that every such
M decomposes into polyhedra bounded by crooked planes, corresponding to an
ideal triangulation of S. This paper classifies and analyzes the structure of
crooked ideal triangles, which play the same role for Margulis spacetimes as
ideal triangles play for hyperbolic surfaces. This extends our previous work on
affine deformations of three-holed sphere and two-holed cross surfaces.
