  We performed multi-frequency studies on the gigahertz-peaked spectrum
high-redshift quasar 0858-279. Initially, the source presented itself at early
VLBI images as a very peculiar resolved blob. We observed the quasar with the
VLBA at 1.4-24 GHz in dual-polarization mode. The high spatial resolution and
spectral index maps enabled us to resolve the core-jet structure and locate a
weak and compact core by its inverted spectrum. The dominant jet component 20
parsecs away from the core was found to be optically thin above 10 GHz and
opaque below it. We also estimated an uncommonly strong magnetic field in the
bright jet feature which turned out to be around 3 G. Faraday rotation measure
maps revealed high RM values over 6000 rad/m^2. Additionally, these maps
allowed us to follow the magnetic field direction in the bright jet feature
being perpendicular to the propagation direction of the jet. All the results
strongly indicated the formation of a shock wave in the dominant component
arising from an interaction with the surrounding matter. Using the proposed
hypothesis as well as the core shift approach, we discovered that the magnetic
field in the core region is of the order of 0.1 G.
