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JWST has revealed a class of numerous, extremely compact sources, withrest-frame red optical/near-infrared (NIR) and blue ultraviolet (UV) colours,nicknamed "little red dots". We present one of the highest signal-to-noiseratio JWST NIRSpec/PRISM spectra of a little red dot, J0647_1045 at $z = 4.5321\pm 0.0001$, and examine its NIRCam morphology, to differentiate the origin ofthe UV and optical/NIR emission, and elucidate the nature of the little red dotphenomenon. J0647_1045 is unresolved ($r_e < 0.17$ kpc) in the three NIRCamlong-wavelength filters, but significantly extended ($r_e = 0.45 \pm 0.06$ kpc)in the three short-wavelength filters, indicating a red compact source in ablue star-forming galaxy. The spectral continuum shows a clear change in slope,from blue in the optical/UV, to red in the restframe optical/NIR, consistentwith two distinct components, fit by power-laws with different attenuation:$A_V = 0.54 \pm 0.01$ (UV) and $A_V = 5.7 \pm 0.2$ (optical/NIR). Fitting theH$\alpha$ line requires both broad (full width at half-maximum $\sim 4300 \pm300 km s^{-1}$) and narrow components, but none of the other emission lines,including H$\beta$, show evidence of broadness. We calculate $A_V = 1.1 \pm0.2$ from the Balmer decrement using narrow H$\alpha$ and H$\beta$, and $A_V >4.1 \pm 0.2$ from broad H$\alpha$ and upper limit on broad H$\beta$, consistentwith the blue and red continuum attenuation respectively. Based on single-epochH$\alpha$ linewidth, the mass of the central black hole is $8 \pm 1 \times 10^8M_\odot$. Our findings are consistent with a multi-component model, where theoptical/NIR and broad lines arise from a highly obscured, spatially unresolvedregion, likely a relatively massive active galactic nucleus, while the lessobscured UV continuum and narrow lines arise, at least partly, from a small butspatially resolved star-forming host galaxy.

Deciphering the JWST spectrum of a 'little red dot' at $z \sim 4.53$: An obscured AGN and its star-forming host