  We present the first dynamical simulation that recreates the major properties
of the archetypal nearby spiral galaxy M101. Our model describes a grazing but
relatively close (14 kpc) passage of the companion galaxy NGC 5474 through
M101's outer disk approximately 200 Myr ago. The passage is retrograde for both
disks, which yields a relatively strong gravitational response while
suppressing the formation of long tidal tails. The simulation reproduces M101's
overall lopsidedness, as well as the extended NE Plume and sharp western edge
of the galaxy's disk. The post-starburst populations observed in M101's NE
Plume are likely a result of star formation triggered at the point of contact
where the galaxies collided. Over time, this material will mix azimuthally,
leaving behind diffuse, kinematically coherent stellar streams in M101's outer
disk. At late times after the encounter, the density profile of M101's disk
shows a broken "upbending" profile similar to those seen in spiral galaxies in
denser environments, further demonstrating the connection between interactions
and long-term structural changes in galaxy disks.
