  We identify a particular mouse, $M^{\text{ld}}$, the minimal ladder mouse,
that sits in the mouse order just past $M_n^{\sharp}$ for all $n$, and we show
that $\mathbb{R}\cap M^{\text{ld}} = Q_{\omega+1}$, the set of reals that are
$\Delta^1_{\omega+1}$ in a countable ordinal. Thus $Q_{\omega+1}$ is a mouse
set. This is analogous to the fact that $\mathbb{R}\cap M^{\sharp}_1 = Q_3$
where $M^{\sharp}_1$ is the the sharp for the minimal inner model with a Woodin
cardinal, and $Q_3$ is the set of reals that are $\Delta^1_3$ in a countable
ordinal. More generally $\mathbb{R}\cap M^{\sharp}_{2n+1} = Q_{2n+3}$. The
mouse $M^{\text{ld}}$ and the set $Q_{\omega+1}$ compose the next natural pair
to consider in this series of results. Thus we are proving the mouse set
theorem just past projective. Some of this is not new. $\mathbb{R}\cap
M^{\text{ld}} \subseteq Q_{\omega+1}$ was known in the 1990's. But
$Q_{\omega+1} \subseteq M^{\text{ld}}$ was open until Woodin found a proof in
2018. The main goal of this paper is to give Woodin's proof.
