The assembly of the record-low total column ozone observed over Europe on 30 November 1999 is investigated using a three-dimensional reconstruction based on POAM, SAGE, and HALOE data and a passive tracer advected by UKMO winds on isentropic surfaces. The reconstruction reproduces TOMS observation to within 10--20 DU over the northern hemisphere and agrees well with select ozonesonde profiles in the mid- to high latitudes, although values in the vicinity of the ozone minimum are systematically higher than TOMS. Relative role is quantified for the disparate dynamical processes that contributed constructively to the low-ozone episode: poleward intrusion of ozone-poor subtropical air in the lowermost stratosphere, adiabatic lifting of ozone maximum, and displacement of ozone-poor Arctic vortex air aloft. Of these, the first two are found to account for about three quarters of the reconstructed column anomaly between 320 and 1900 K whereas the last for about one quarter.