  A direct consequence of Faraday rotation is that the polarized radio sky does
not resemble the total intensity sky at long wavelengths. We analyze G137+7,
which is undetectable in total intensity but appears as a depolarization
feature. We use the first polarization maps from the Canadian Hydrogen
Intensity Mapping Experiment. Our $400-729$ MHz bandwidth and angular
resolution, $17'$ to $30'$, allow us to use Faraday synthesis to analyze the
polarization structure. In polarized intensity and polarization angle maps, we
find a "tail" extending $10^\circ$ from the "head" and designate the combined
object the "tadpole". Similar polarization angles, distinct from the
background, indicate that the head and tail are physically associated. The head
appears as a depolarized ring in single channels, but wideband observations
show that it is a Faraday rotation feature. Our investigations of H I and
H$\alpha$ find no connections to the tadpole. The tail suggests motion of
either the gas or an ionizing star through the ISM; the B2(e) star HD 20336 is
a candidate. While the head features a coherent, $\sim -8$ rad m$^2$ Faraday
depth, Faraday synthesis also identifies multiple components in both the head
and tail. We verify the locations of the components in the spectra using QU
fitting. Our results show that $\sim$octave-bandwidth Faraday rotation
observations at $\sim 600$ MHz are sensitive to low-density ionized or
partially-ionized gas which is undetectable in other tracers.
