The author has recently shown that the spectra of quasi-stellar objects can be explained by the hypotheses that there is no red shift and that the strength of emission lines is due to laser action. A realistic model of the QSOs, based on these hypotheses is proposed. A QSO is a star with a rapidly expanding atmosphere, in which population inversion is occurring. This atmosphere can be approximated by a decaying plasma. Properties of such a plasma are reviewed. A given transition in an atom can undergo laser action only within narrow ranges of the electron density (ne), electron temperature (Te) and the density of the ground state atoms (n(1)). ne, Te, n(1) plot is introduced to classify the QSOs. Consequences of the proposed model are discussed. Intensity variations of the same line in different QSOs, and also in the same QSO, are shown to follow naturally from this model. Quantization in the red-shift is explained. Polarization of strong emission lines is predicted.