  We explore aspects of the correspondence between Seifert 3-manifolds and 3d
$\mathcal{N}=2$ supersymmetric theories with a distinguished abelian flavour
symmetry. We give a prescription for computing the squashed three-sphere
partition functions of such 3d $\mathcal{N}=2$ theories constructed from
boundary conditions and interfaces in a 4d $\mathcal{N}=2^*$ theory, mirroring
the construction of Seifert manifold invariants via Dehn surgery. This is
extended to include links in the Seifert manifold by the insertion of
supersymmetric Wilson-'t Hooft loops in the 4d $\mathcal{N}=2^*$ theory. In the
presence of a mass parameter for the distinguished flavour symmetry, we recover
aspects of refined Chern-Simons theory with complex gauge group, and in
particular construct an analytic continuation of the $S$-matrix of refined
Chern-Simons theory.
