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.
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