  Seen from the modern lens of causal inference, Bell's theorem is nothing else
than the proof that a specific classical causal model cannot explain quantum
correlations. It is thus natural to move beyond Bell's paradigmatic scenario
and consider different causal structures. For the specific case of three
observable variables, it is known that there are three non-trivial causal
networks. Two of those, are known to give rise to quantum non-classicality: the
instrumental and the triangle scenarios. Here we analyze the third and
remaining one, which we name the Evans scenario, akin to the causal structure
underlying the entanglement-swapping experiment. We prove a number of results
about this elusive scenario and introduce new and efficient computational tools
for its analysis that also can be adapted to deal with more general causal
structures. We do not solve its main open problem -- whether quantum
non-classical correlations can arise from it -- but give a significant step in
this direction by proving that post-quantum correlations, analogous to the
paradigmatic Popescu-Rohrlich box, do violate the constraints imposed by a
classical description of Evans causal structure.
