  We study the retardation regime of doped graphene plasmons, given by the
nominal crossing of the unretarded plasmon and light-cone. In addition to
modifications in the plasmon dispersion relation, retardation implies strong
coupling between propagating light and matter, even for homogeneous graphene,
which opens up the possibility of efficient plasmonics in simple graphene
devices. We exemplify this enhancement in a double-layer configuration that
exhibits {\em perfect} (if lossless) light transmissions across a classically
forbidden region, providing a simpler analog of the corresponding phenomenon in
perforated metal sheets. We also show that (broad) Fabry-P\'erot resonances
present without graphene turn into sharply peaked, quasi-discrete modes in the
presence of graphene where graphene's response function is given by the typical
Fano lineshape.
