Start brown thread at the eye and wind back to the bend, keeping the base thin. A spinner is a fly of almost nothing, and every wrap shows in the water print.
Tie in a few Coq de Leon Indio barbs as a long splayed tail, at least a shank and a half. Stiff CdL fibres hold the flat, spent posture on the surface.
Tie a long tobacco CDC feather in by the tip at the bend and wind it forward in touching turns to the 65% mark as the body. A CDC body floats the rear of the fly on its own, which is exactly what a spinner needs since it carries no hackle.
Stroke the body barbs back and secure, then tie two natural grey CDC feathers in crosswise at the 70% mark with figure-eight wraps so they lie flat out to each side as spent wings.
Trim the wings to roughly a shank length each side and even them up. The silhouette is the fly's entire identity to a fish looking up.
Build a small head and whip finish. Angle the wings slightly up instead of flat and the same fly fishes as a dun, so one tie covers both stages of an evening rise.