We present a simple UV completion of the Nelson-Barr solution of the strong CP problem. We focus on the minimal implementation of the Nelson-Barr construction where the visible sector contains only one extra pair of right-handed vector-like up/down quarks. In our UV completion, the CP symmetry is spontaneously broken by the dynamics of a hidden QCD at $\theta=\pi$. The latter possesses only heavy degrees of freedom which do not affect the visible sector phenomenology. The CP violation is mediated via a scalar portal to the visible sector in such a way that the CKM phase is of order one while the strong CP phase is parametrically suppressed.  An explicit UV completion allows us to control UV threshold corrections induced by Planck suppressed operators and pinpoint the region of parameter space which is theoretically most appealing.