  Evidence is presented for standard model production of a Z boson in
association with a single top quark. The analysis uses a data sample of
proton-proton collisions at $\sqrt{s} = 13$ TeV recorded in 2016 by the CMS
detector, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Final
states containing three leptons (electrons or muons) and at least two jets are
investigated, and the measured cross section is $\sigma($pp $\rightarrow$ tZq
$\rightarrow $Wb$\ell^{+}\ell^{-}$q) = 123$^{+44}_{-39}$ fb, where $\ell$
stands for electrons, muons or taus. The corresponding observed (expected)
significance is 3.7 (3.1) standard deviations.
