An amplitude analysis of decays together with a measurement of the polarization vector in semiōleptonic beauty hadron decays is presented. A sample of 400 000 candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the state are also determined. A significant polarization is found. A large sensitivity of the decay to the polarization is seen, making the amplitude model suitable for polarization measurements in other systems.