Context : While there is growing consensus on the existence of numerous dust–enshrouded red quasars , their discovery and detailed exploration is still an observational challenge .
In the course of the near–mid–infrared AGN search combining the 6.7 \mu m ISOCAM Parallel Survey and 2MASS we have discovered 24 type –1 quasars about a third of which are too red to be discriminated by optical/UV search techniques .

Aims : Here we report on a detailed case study of the reddest type –1 quasar of our sample , 2MASS J23410667 - 0914327 ( for short J2341 ) at redshift z = 0.236 with M _ { K } = -25.8 and J - K _ { s } = 1.95 .
This source has a very red optical appearance but lacks the far-infrared emission typically seen in known dust enshrouded AGN .
Therefore we here explore its enigmatic nature .

Methods : We performed spectroscopy in the optical with VLT/FORS1 and in the mid–infrared ( 5 - 38 \mu m ) with the Spitzer Space Telescope as well as near–infrared ( NIR ) imaging with ISPI at the CTIO 4m–telescope .
To explain the red optical continuum of the quasar we examine nuclear dust reddening of an intrinsically blue quasar continuum in combination with dilution by stellar light of the host galaxy .

Results : The optical and NIR observations reveal a star forming emission–line galaxy at the same redshift as the quasar with a projected linear separation of 1 \aas@@fstack { \prime \prime } 8 ( 6.7 kpc ) .
The quasar and its companion are embedded in diffuse extended continuum emission .
Compared with its companion the quasar exhibits redder optical–NIR colours , which we attribute to hot nuclear dust .
The mid–infrared spectrum shows only few emission lines superimposed on a power–law spectral energy distribution typically seen in type –1 AGN .
However , the lack of strong far–infrared emission suggests that our potentially interacting object contains much less gas and dust and is in a stage different from dust reddened ULIRG–AGN like Mrk 231 .
The optical spectrum shows signatures for reddening in the emission–lines and no post–starburst stellar population is detected in the host galaxy of the quasar .
The optical continuum emission of the active nucleus appears absorbed and diluted .

Conclusions : Even the combination of absorption and host dilution is not able to match J2341 with standard quasar templates .
While the BLR shows only a rather moderate absorption of E _ { B - V } = 0.3 , the continuum shorter than 4500 \AA requires strong obscuration with E _ { B - V } = 0.7 , clearly exceeding the constraints from the low upper limit on the silicate 9.7 \mu m absorption .
This leads us to conclude that the continuum of the quasar J2341 is intrinsically redder than that of typical quasars .