  The recently introduced anomaly-free twistor string in 4 dimensions is
further explored. The spectrum based on the physical states and its Minkowski
interpretation are examined. Scattering amplitudes with vertex operators
involving gravitons and fermions are computed and are compared with
Einstein-Yang-Mills amplitudes. Tree and one-loop scattering amplitudes are
shown to have proper unitary factorization properties. Finally a string field
theory is proposed.
