  After 15 years, in late 2018, the magnetar XTE J1810-197 underwent a second
recorded X-ray outburst event and reactivated as a radio pulsar. We initiated
an X-ray monitoring campaign to follow the timing and spectral evolution of the
magnetar as its flux decays using Swift, XMM-Newton, NuSTAR, and NICER
observations. During the year-long campaign, the magnetar reproduced similar
behaviour to that found for the first outburst, with a factor of two change in
its spin-down rate from $\sim7.2\times10^{-12}$ s s$^{-1}$ to
$\sim1.5\times10^{-11}$ s s$^{-1}$ after two months. Unique to this outburst,
we confirm the peculiar energy-dependent phase shift of the pulse profile.
Following the initial outburst, the spectrum of XTE J1810-197 is well-modelled
by multiple blackbody components corresponding to a pair of non-concentric, hot
thermal caps surrounded by a cooler one, superposed to the colder star surface.
We model the energy-dependent pulse profile to constrain the viewing and
surface emission geometry and find that the overall geometry of XTE J1810-197
has likely evolved relative to that found for the 2003 event.
