Context :

Aims : We aim to understand the real nature of the stellar overdensity at southern galactic latitudes in the region of CMa .

Methods : We perform a critical re-analysis and discussion of recent results presented in the literature which interpret the CMa overdensity as the signature of an accreting dwarf galaxy or a new substructure within the Galaxy .
Several issues are addressed .

Results : We show that arguments against the “ warp ” interpretation are based on an erroneous perception of the Milky Way .
There is nothing anomalous with colour–magnitude diagrams on opposite sides of the average warp mid-plane being different .
We witnessed the rise and fall of the blue plume population , first attributed to young stars in a disrupting dwarf galaxy and now discarded as a normal disc population .
Similarly , there is nothing anomalous in the outer thin+thick disc metallicities being low ( -1 < [ Fe/H ] < -0.5 ) , and spiral arms ( as part of the thin disc ) should , and do , warp .
Most importantly , we show unambiguously that , contrary to previous claims , the warp produces a stellar overdensity that is distance-compatible with that observed in CMa .

Conclusions : The CMa over-density remains fully accounted for in a first order approach by Galactic models without new substructures .
Given the intrinsic uncertainties ( concerning the properties of the warp , flare and disc cutoff , the role of extinction and degeneracy ) , minor deviations with respect to these models are not enough to support the hypothesis of an accreted dwarf galaxy or new substructure within the Milky Way disc .