1 Introduction

In the course of the ISOCAM Core Programme devoted to the observation of $z\sim 0.2$ galaxy clusters (DEEPXSRC), we have discovered a faint field source at 7.5 and 15 $\mu$m with no obvious counterpart on medium deep optical images. This object was thus a potential "extremely red object" (ERO), but for the first time, being directly unveiled through mid-infrared (MIR) observations. The new ERO class, usually defined by R-K > 5 or R-K > 6, is not only rapidly growing in size but also in astrophysical relevance. Indeed, it may shed light on the still hotly debated question of AGN/starburst connections, the formation epoch of ellipticals as well as the existence of dust within the crucial redshift range 1 < z < 3. For an up-to-date review on the ERO topic, see for instance Liu et al. (2000). Here, we describe the follow-up observations we have undertaken in order to determine the redshift and to shed light on the nature of this peculiar object. The next section presents the spectroscopic and photometric data from X-ray to radio wavelengths. Section 3 discusses possible interpretations in conjunction with information provided by galaxies and other EROs at comparable redshift. Throughout the paper, we assume H₀ = 75 kms^-1Mpc^-1and q₀ = 0.