  Sh 2-188 is an example of strong interaction between a planetary nebula (PN)
and the interstellar medium (ISM). Its structure is postulated to be the result
of motion through the ISM. We present new H$\alpha$ images from the Isaac
Newton Telescope Photometric H$\alpha$ Survey of the Northern Galactic Plane
which reveal new structure. The nebula extends 15 arcmin on the sky in total.
We have developed a `triple-wind' hydrodynamical model, comprising of the
initial `slow' asymptotic giant branch (AGB) wind and the later `fast' stellar
wind plus a third wind reflecting the motion through the ISM. Simulations at
various velocities of the central star relative to the ISM indicate that a high
velocity of 125 kms is required to reproduce the observed structure. We find
most of the structure already forms during the AGB phase. The closure of the
ring arises from the slow--fast wind interaction. Most of the mass lost on the
AGB has been swept downstream, providing a potential explanation of the missing
mass problem in PNe. We report a proper motion for the central star of 30 mas
yr^-1 in the direction of the bright limb, implying a distance to the nebula of
850^{+500}_{-420} pc, consistent with a spectroscopic distances. Expansion
velocities measured from spectroscopic data are consistent with velocities
measured from the simulation. The model shows that the size of the PN was
already set during the AGB phase.
