  Phase-space data, chemistry, and ages together reveal a complex structure in
the outer low-${\alpha}$ disc of the Milky Way. The age-vertical velocity
dispersion profiles beyond the Solar Neighbourhood show a significant jump at 6
Gyr for stars beyond the Galactic plane. Stars older than 6 Gyr are
significantly hotter than younger stars. The chemistry and age histograms
reveal a bump at [Fe/H] = -0.5, [${\alpha}$/Fe] = 0.1, and an age of 7.2 Gyr in
the outer disc. Finally, viewing the stars beyond 13.5 kpc in the
age-metallicity plane reveals a faint streak just below this bump, towards
lower metallicities at the same age. Given the uncertainty in age, we believe
these features are linked and suggest a pericentric passage of a massive
satellite 6 Gyr ago that heated pre-existing stars, led to a starburst in
existing gas. New stars also formed from the metal-poorer infalling gas. The
impulse approximation was used to characterise the interaction with a
satellite, finding a mass of ~1e11 M$_{\odot}$, and a pericentric position
between 12 and 16 kpc. The evidence points to an interaction with the
Sagittarius dwarf galaxy, likely its first pericentric passage.
