The small-amplitude Cepheid V1726 Cyg and two members of open cluster Platais 1 (Platais 1 star No. 1 (1921) and Platais 1 star No. 111 (1600)) were investigated, using high-resolution CCD spectra. The following results were obtained: 1) All objects have the same metallicities, close to that of the Sun (for V1726 Cyg weighted average [ Fe/H$]=+0.05$, for Platais 1 star No. 1 (1921) [ Fe/H$]=+0.13$); 2) values of T eff and $\log g$ for the B-stars are in excellent agreement with those determined from $(B-V)$ colour indices using a $(B-V)\sim(T_{\rm eff}$, $\log g$) calibration; 3) the elemental abundances indicate that V1726 Cyg is in the post first dredge-up stage with an age near $1.5 \times 10^{8}$, and is crossing the Cepheid instability strip for the third time. Mean values of $T_{\rm eff}=6100$ K and $\log g=2.35 \pm 0.05$ permit us to refine its colour excess to $E_{B-V}=0\fm 33$, which for a distance of $d = 1568\pm 13$ pc corresponds to $M_{V}=-2\fm 99$. The Cepheid could therefore be pulsating in the fundamental tone, although pulsation in the first overtone is not excluded; 4) Platais 1 star No. 1 (1921) is a slowly rotating HgMn-star with a high helium content, while Platais 1 star No. 111 (1600) is a rapidly rotating main-sequence star with a helium content comparable to that of the Sun; 5) the age of the open cluster is estimated to be about $2.5 \times 10^{8}$ yr.