We consider a PT -symmetric cubic oscillator with an imaginary double well. We prove the existence of an infinite number of level crossings with a definite selection rule. Decreasing the positive parameter from large values, at a parameter n we find the crossing of the pair of levels (E 2n+1 ( ), E 2n ( )) becoming the pair of levels (E + n ( ), E − n ( )). For large parameters, a level is a holomorphic function E m ( ) with different semiclassical behaviors, E ± j ( ), along different paths. The corresponding m-nodes delocalized state ψ m ( ) behaves along the same paths as the semiclassical j-nodes states ψ ± j ( ), localized at one of the wells x ± respectively. In particular, if the crossing parameter n is by-passed from above, the levels E 2n+(1/2)±(1/2) ( ) have respectively the semiclassical behaviors of the levels E ∓ n ( ) along the real axis. These results are obtained by the control of the nodes. There is evidence that the parameters n accumulate at zero and the accumulation point of the corresponding energies is an instability point of a subset of the Stokes complex called the monochord, consisting of the vibrating string and the sound board.