We present infrared spectroscopy of the 2019 eruption of the recurrent nova V3890 Sgr, obtained over the period 5.1–46.3 days after the eruption. The spectrum of the red giant became more prominent as the flux declined, and by day 46.3 dominated the spectrum. Hydrogen and helium emission lines consisted of a narrow component superposed on a broad pedestal. The full width at half maximum of the narrow components declined with time t as the eruption progressed, as t-0.74, whereas those of the broad components remained essentially constant. Conversely, the line fluxes of the narrow components of Pa ß remained roughly constant, while those of the broad components declined by a factor ~ 30 over a period of <~ 25 days. The behaviour of the broad components is consistent with them arising in unencumbered fast-flowing ejecta perpendicular to the binary plane, in material that was ejected in a short ~ 3.3-day burst. The narrow components arise in material that encounters the accumulated circumstellar material. The outburst spectra were rich in coronal lines. There were two coronal line phases, one that originated in gas ionised by supersoft X-ray source, the other in shocked gas. From the relative fluxes of silicon and sulphur coronal lines on day 23.4 – when the emitting gas was shocked – we deduce that the temperature of the coronal gas was 9.3 × 105 K, and that the abundances are approximately solar.