  The advent of space-based photometry provides the opportunity for the first
precise characterizations of variability in Mercury-Manganese (HgMn/CP3) stars,
which might advance our understanding of their internal structure. We have
carried out a spectroscopic and photometric investigation of the candidate CP3
star KIC 6128830. A detailed abundance analysis based on newly-acquired
high-resolution spectra was performed, which confirms that the star's abundance
pattern is fully consistent with its proposed classification. Photometric
variability was investigated using four years of archival Kepler data. In
agreement with results from the literature, we have identified a single
significant and independent frequency $f_1$=0.2065424 d$^{-1}$ with a
peak-to-peak amplitude of $\sim$3.4 mmag and harmonic frequencies up to $5f_1$.
Drawing on the predictions of state-of-the-art pulsation models and information
on evolutionary status, we discuss the origin of the observed light changes.
Our calculations predict the occurrence of g-mode pulsations at the observed
variability frequency. On the other hand, the strictly mono-periodic nature of
the variability strongly suggests a rotational origin. While we prefer the
rotational explanation, the present data leave some uncertainty.
