We present the discovery of AT 2024wpp (‘Whippet’), a fast and luminous 18cow-like transient. At a redshift of (Formula presented), revealed by Keck Cosmic Web Imager spectroscopy of its faint star-forming host, it is the fourth-nearest example of its class to date. Rapid identification of the source in the Zwicky Transient Facility data stream permitted ultraviolet-through-optical observations to be obtained prior to peak, allowing the first determination of the peak bolometric luminosity ((Formula presented) erg s(Formula presented) ), maximum photospheric radius ((Formula presented) cm), and total radiated energy ((Formula presented) erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-ultraviolet spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending (Formula presented) 100 d post-explosion from the Very Large Telescope, Hubble Space Telescope, Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a rapidly accreting central engine blows a fast ((Formula presented) 0.2 c) wind into the surrounding medium and irradiates it with X-rays. The high Doppler velocities and intense ionization within this wind prevent identifiable spectroscopic features from appearing in the ejecta or in the surrounding circumstellar material. Weak H and He signatures do emerge in the spectra after 35 d in the form of double-peaked narrow lines. Each peak is individually narrow (full width (Formula presented) km s(Formula presented) ) but the two components are separated by (Formula presented) km s(Formula presented), indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.