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We report the detection of a strong HI 21-cm absorption system at z=0.5344,as well as a candidate system at z=0.3389, in the sight-line towards the z=2.64quasar MG J0414+0534. This, in addition to the absorption at the host redshiftand the other two intervening absorbers, takes the total to four (possiblyfive). The previous maximum number of 21-cm absorbers detected along a singlesight-line is two and so we suspect that this number of gas-rich absorbers isin some way related to the very red colour of the background source. Despitethis, no molecular gas (through OH absorption) has yet been detected at any ofthe 21-cm redshifts, although, from the population of 21-cm absorbers as awhole, there is evidence for a weak correlation between the atomic linestrength and the optical--near-infrared colour. In either case, the fact thatso many gas-rich galaxies (likely to be damped Lyman-alpha absorption systems)have been found along a single sight-line towards a highly obscured source mayhave far reaching implications for the population of faint galaxies notdetected in optical surveys, a possibility which could be addressed throughfuture wide-field absorption line surveys with the Square Kilometre Array.

A fourth HI 21-cm absorption system in the sight-line of MG J0414+0534: a record for intervening absorbers