Call value plotted against spot, futures and expiry price

Draw three graphs for a European call on a non-dividend stock: (i) its payoff at expiry as a function of the terminal stock price; (ii) its value before expiry as a function of the futures price on the stock; (iii) its value before expiry as a function of the spot price. How are the three curves related?

(i) is the hockey stick $\max(S_T-K,0)$; (ii) and (iii) are smooth convex curves. Against spot, the pre-expiry value lies above $\max(S - Ke^{-rT},0)$ and hence above intrinsic value, approaching $S - Ke^{-rT}$ for deep in-the-money calls. Since $F = Se^{rT}$, graph (ii) is the same curve on a rescaled axis: $C = e^{-rT}[F N(d_1) - K N(d_2)]$, which approaches $e^{-rT}(F-K)$ and so dips below the futures intrinsic value $F-K$ when deep in the money.