We propose a three-slot amplify-and-forward cooperative diversity scheme for a half-duplex two-relay channel. It is shown that the proposed scheme outperforms the four-slot scheme proposed by Azarian et al. in terms of the diversity-multiplexing tradeoff, which is the best known in the literature. Numerical simulation results show that significant power gain can be obtained from the proposed scheme over the four-slot scheme in terms of both the outage probability and the error rate in the case where a "perfect" space-time code is used.