ESO 243-49 is a high-mass (circular velocity $v_{rm c}approx200,{rm km,s^{-1}}$) edge-on S0 galaxy in the Abell 2877 cluster at a distance of $sim95,{rm Mpc}$. To elucidate the origin of its thick disc, we use MUSE science verification data to study its kinematics and stellar populations. The thick disc emits $sim80%$ of the light at heights in excess of $3.5^{primeprime}$ ($1.6,{rm kpc}$). The rotation velocities of its stars lag by $30-40,{rm km,s^{-1}}$ compared to those in the thin disc, which is compatible with the asymmetric drift. The thick disc is found to be more metal-poor than the thin disc, but both discs have old ages. We suggest an internal origin for the thick disc stars in high-mass galaxies. We propose that the thick disc formed either ${rm a)}$ first in a turbulent phase with a high star formation rate and that a thin disc formed shortly afterwards, or ${rm b)}$ because of the dynamical heating of a thin pre-existing component. Either way, the star formation in ESO 243-49 was quenched just a few Gyrs after the galaxy was born and the formation of a thin and a thick disc must have occurred before the galaxy stopped forming stars. The formation of the discs was so fast that it could be described as a monolithic collapse where several generations of stars formed in a rapid succession.
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