  I present the moduli space of the (2+2)-dimensional critical closed fermionic
string with two world-sheet supersymmetries. The integration of fermionic and
Maxwell moduli in the presence of punctures yields the string measure for
n-point amplitudes at arbitrary genus and instanton number. Generalized
picture-changing and spectral-flow operators emerge, connecting different
instanton sectors. Tree and loop amplitudes are computed.
