  The advancement of technologies for the precise interrogation of molecules
offers exciting possibilities for new studies in the realms of precision
spectroscopy and quantum technologies. Experiments in these domains often
address molecular vibrations in the mid-infrared (MIR) spectral region, thus
generating the need for spectrally pure and accurate MIR laser sources.
Quantum-cascade lasers (QCLs) have emerged as flexible sources of coherent
radiation available over a wide range of MIR frequencies. Here, we demonstrate
a robust approach for the simultaneous linewidth narrowing, frequency
stabilisation, and absolute frequency referencing of MIR QCLs all of which are
prerequisites for precise spectroscopic experiments. Following upconversion of
its radiation to the visible domain, we implement a phase lock of the QCL to a
linewidth-narrowed optical frequency comb which is referenced to a remote
SI-traceable primary frequency standard via a fibre link for absolute frequency
calibration. To achieve a reliable frequency counting of the beat note between
the QCL and the OFC, we employ redundant tracking oscillators and demonstrate a
frequency instability of $5\times10^{-13}$ at 1 s and $2\times10^{-14}$ at 1000
s integration time, limited by the accuracy of our remote reference.
