We report the results of our study of the high-velocity ( \approx 160 km s ^ { -1 } ) runaway O star CPD - 64°2731 and its associated horseshoe-shaped nebula discovered with the Wide-field Infrared Survey Explorer . Spectroscopic observations with the Southern African Large Telescope and spectral analysis indicate that CPD - 64°2731 is a fast-rotating main-sequence O5.5 star with enhanced surface nitrogen abundance . We derive a projected rotational velocity of \approx 300 km s ^ { -1 } which is extremely high for this spectral type . Its kinematic age of \approx 6 Myr , assuming it was born near the Galactic plane , exceeds its age derived from single star models by a factor of two . These properties suggest that CPD - 64°2731 is a rejuvenated and spun-up binary product . The geometry of the nebula and the almost central location of the star within it argue against a pure bow shock interpretation for the nebula . Instead , we suggest that the binary interaction happened recently , thereby creating the nebula , with a cavity blown by the current fast stellar wind . This inference is supported by our results of 2D numerical hydrodynamic modelling .