  Classical novae are quite frequent in M~31. However, very few spectra of M31
novae have been studied to date, especially during the early decline phase. Our
aim is to study the photometric and spectral evolution of a M31 nova event
close to outburst. We present photometric and spectroscopic observations of
M31N 2005-09c, a classical nova in the disk of M31, using the 1.3m telescope of
the Skinakas Observatory in Crete (Greece), starting on the 28th September,
i.e. about 5 days after outburst, and ending on the 5th October 2005, i.e.
about 12 days after outburst. We also have supplementary photometric
observations from the La Sagra Observatory in Northern Andalucia, Spain, on
September 29 and 30, October 3, 6 and 9 and November 1, 2005. The wavelength
range covered by the spectra is from 3565 A to 8365 A. The spectra are of high
S/N allowing the study of the evolution of the equivalent widths of the Balmer
lines, as well as the identification of non-Balmer lines. The nova displays a
typical early decline spectrum that is characterized by many weak FeII
multiplet emissions. It is classified as a P$_{fe}$ nova. From the nova light
curve, we have also derived its speed class, t=14+-2.5 days. As the nova
evolved the Balmer lines became stronger and narrower. The early decline of the
expansion velocity of the nova follows a power law in time with an exponent of
\~-0.2.
