the branching ratio we use the Monte Carlo generated efficiency, shown in Fig. \[beff\_ds4pi\_kpi\] as a function of $(4\pi)^-$ mass. The efficiency falls off at larger $(4\pi)^-$ masses because the detection of the slow $\pi^+$ from the $D^{*+}$ decay becomes increasingly difficult. Since the efficiency varies with mass we need to determine the $(4\pi)^-$ mass spectrum. To rid ourselves of the problem of the background shape, we fit the $B$ candidate mass spectrum in 50 MeV bins of $(4\pi)^-$ mass. (The mass resolution is approximately 12 MeV.) The resulting $(4\pi)^-$ mass spectrum is shown in Fig. \[m4pi\_ds4pi\_kpi\]. There are indications of a low mass structure around 1.4 GeV. This will be investigated further in this paper.

We find $${\cal B}(\overline{B}^o\to D^{*+}\pi^+\pi^+\pi^-\pi^o)
=(1.72\pm 0.14\pm 0.24)\%~~~.$$

The systematic error arises mainly from our lack of knowledge about the tracking and $\pi^o$ efficiencies. We assign errors of $\pm$2.2% on the efficiency of each charged track, $\pm$5% for the slow pion from the $D^{*+}$, and $\pm$5.4% for the $\pi^o$. The error due to the background shape is evaluated in three ways. First of all, we change the background shape by varying the fitted parameters by 1$\sigma$. This results in a change of $\pm$3%. Secondly, 