  We study the Sturm--Liouville operator $$
  T(\varepsilon)y=-\frac{1}{\varepsilon}y''+ p(x)y, $$ with concrete
$\mathcal{PT}$-- symmetric potential $p(x) = ix$ and Dirichlet boundary
conditions on the segment $[-1,1]$. Here $\varepsilon \in (0, \infty)$ is a
physical parameter. We explicitly describe a beautiful phenomenon of the
eigenvalue behavior when $\varepsilon$ changes from $0$ to $\infty$. All the
critical values of $\varepsilon$ which determine the eigenvalue dynamics, are
found in terms of the special Airy functions.
