We present a novel method to investigate c reionization, using joint spectral information on high-redshift Lyman α emitters (LAEs) and quasi-stellar objects (QSOs). Although LAEs have been proposed as reionization probes, their use is hampered by the fact their Lyα line is damped not only by intergalactic H i but also internally by dust. Our method allows us to overcome such degeneracy. First, we carefully calibrate a reionization simulation with QSO absorption line experiments. Then we identify LAEs ( and equivalent width >20 Å) in two simulation boxes at z= 5.7 and 6.6 and we build synthetic images/spectra of a prototypical LAE. The surface brightness maps show the presence of a scattering halo extending up to 150 kpc from the galaxye. For each LAE we then select a small box of (10 h−1 Mpc)3 around it and derive the optical depth τ along three viewing axes. At redshift 5.7, we find that the Lyα transmissivity , almost independent of the halo mass. This constancy arises from the conspiracy of two effects: (i) the intrinsic Lyα line width and (ii) the infall peculiar velocity. At higher redshift, z= 6.6, where the transmissivity is instead largely set by the local H i abundance and consequently increases with halo mass, Mh, from 0.15 to 0.3. Although outflows are present, they are efficiently pressure confined by infall in a small region around the LAE; hence they only marginally affect transmissivity. Finally, we cast line of sight originating from background QSOs passing through foreground LAEs at different impact parameters, and compute the quasar transmissivity (). At small impact parameters, d < 1 cMpc, a positive correlation between and Mh is found at z= 5.7, which tends to become less pronounced (i.e. flatter) at larger distances. Quantitatively, a roughly 10× increase (from 5 × 10−3 to 6 × 10−2) of is observed in the range log Mh= (10.4–11.6). This correlation becomes even stronger at z= 6.6. By cross-correlating and , we can obtain a H i density estimate unaffected by dust. At z= 5.7, the cross-correlation is relatively weak, whereas at z= 6.6 we find a clear positive correlation. We conclude by briefly discussing the perspectives for the application of the method to existing and forthcoming data.