The molecule is shown in the textbook as:
I can rationalise that the N is sp2 hybridised with a single electron in the p-orbital perpendicular to the plane of the S/N ring. (The sp2 lone pair is omitted for clarity) The S atom is thought to be sp3 hybridised, but how can this explain the double bond formed with N? Can an sp2 and sp3 orbital overlap??