  Dispersion theory is used to provide a model-independent low-energy
representation of the three electromagnetic isovector transition form factors
$N^{*}(1520)\to N$. At low energies the virtual photon couples dominantly to a
pion pair. Taking the very well understood pion vector form factor and pion
re-scattering into consideration, the determination of the transition form
factors is traced back to the determination of pion-baryon scattering
amplitudes. Their low-energy aspects are parametrized by baryon exchange,
accounting for the main decay channels of the $N^*(1520)$. Short-distance
physics is encoded in subtraction constants that are fitted to data on
space-like form factors and hadronic decays. It is shown that a limitation in
the determination of the subtraction constants lies in the fact that isovector
form factors require sufficient information about the differences between
protons and neutrons. In particular, this calls for improvements in the form
factor extraction from the electroproduction of the $N^*(1520)$ on the neutron.
Via the dispersion relations, space- and time-like regions are naturally
connected from first principles. This allows to predict the time-like form
factors that enter the Dalitz decays $N^*(1520)\to N e^- e^+$ and $N^*(1520)\to
N \mu^- \mu^+$. Under the assumption of the dominance of the isovector over the
isoscalar channel, the Dalitz decay distributions are predicted.
