We have identified a new intermediate polar, HS 0943+1404, as part of our ongoing search for cataclysmic variables in the Hamburg Quasar Survey. The orbital and white dwarf spin periods determined from time-resolved photometry and spectroscopy are Porb ≃ 250 min and Pspin= 69.171 ± 0.001 min, respectively. The combination of a large ratio Pspin/Porb≃0.3 and a long orbital period is very unusual compared to the other known intermediate polars. The magnetic moment of the white dwarf is estimated to be μ1˜1034 G cm3, which is in the typical range of polars. Our extensive photometry shows that HS 0943+1404 enters into deep (~3 mag) low states, which are also a characteristic feature of polars. We therefore suggest that the system is a true "intermediate" polar that will eventually synchronise, that is, a transitional object between intermediate polars and polars. The optical spectrum of HS 0943+1404 also exhibits a number of unusual emission lines, most noticeably NIIλ5680, which is likely to reflect enhanced nitrogen abundances in the envelope of the secondary.