Calibrated data and initial results from the multi-slit spectroscopy observations of NGC 891. Panels a and b show the Hα and [N II]λ6583 Å line intensities in arbitrary units. Panel c shows the line centroid velocity jointly estimated from both the Hα and the [N II]λ6583 Å lines. Panel d shows the [N II]λ6583 Å-to-Hα line intensity ratio. The white cross in each panel marks the galactic centre. The cut criteria for panels c and d are S/N_Hα > 6 and S/N${}_{[\mathrm{N}\mathrm{I}\mathrm{I}]\lambda 6583\mathrm{\AA }}>4$. The large number of spurious detections in the halo are caused by the misidentification of the residual sky lines.