  The magnetization, $M(H \leq 30$ T, 0.7 K $\leq T \leq 300$ K), from single
crystals and powder samples of (C$_{5}$H$_{12}$N)$_{2}$CuBr$_{4}$ has been used
to identify this system as an $S=1/2$ Heisenberg two-leg ladder in the strong
coupling limit, $J_{\perp} = 13.3$ K and $J_{\parallel} = 3.8$ K, with $H_{c1}
= 6.6$ T and $H_{c2} = 14.6$ T. An inflection point in $M(H, T = 0.7$ K) at
half-saturation, $M_{s}/2$, is described by an effective \emph{XXZ} chain. The
data exhibit universal scaling behavior in the vicinity of $H_{c1}$ and
$H_{c2}$, indicating the system is near a quantum critical point.
