  The SW Sex stars are a class of cataclysmic variables, originally identified
because they shared a number of enigmatic properties - most notably,
single-peaked emission lines instead of the double-peaked lines one would
expect from their high-inclination accretion discs. We present high
time-resolution spectrophotometry of the eclipsing nova-like variables SW Sex
and DW UMa, two of the founding members of the SW Sex class. Both systems show
single-peaked Balmer and HeII 4686A emission lines that appear to originate
from a region in the disc that lies close to, but downstream of, the bright
spot. The emission-line light curves are consistent with the finding from X-ray
and ultraviolet observations that we predominantly see the flared disc rim and
the unobscured back portion of the disc in these systems. In DW UMa, the HeII
4686A emission line originates from close to the white dwarf and exhibits
flaring. Such flares have been used to argue for magnetically-channelled
accretion, as in the intermediate polars, but the lack of a clear periodicity
in the flares argues for a simpler model in which we are viewing the central
regions of the disc through the non-uniform upper edge of a flared disc rim. We
also observe narrow, blue-shifted, transient absorption features in the Balmer
lines of DW UMa, which we attribute to blobs of material ejected from the
system, possibly by a magnetic propeller, that happen to be passing between us
and the binary. Our results suggest that the solution to the SW Sex enigma is a
combination of dominant bright-spot emission and a self-occulting disc. We also
propose a simplified classification scheme for nova-like variables.
