The paper presents the resolved stellar component and filamentary overdense environment of the Hubble Space Telescope (HST)-dark submillimeter galaxy HDF850.1 at z = 5.18, observed with the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES). HDF850.1 is known for its heavy dust obscuration and is embedded in an overdense environment. Using nine-band NIRCam images, the authors detect and resolve the rest-frame UV-optical counterpart of HDF850.1 into two components due to dust obscuration in the center. The southern component exhibits significant UV and Hα emission, making the galaxy approximately 100 times above the empirical relation between infrared excess and UV continuum slope. The northern component is more attenuated by dust and thus fainter in UV and Hα. The authors construct a spatially resolved dust-attenuation map, which matches well with millimeter interferometry data. The system hosts a stellar mass of 10^10.8±0.1 M☉ and a star formation rate (SFR) of 10^-8.2±0.5 M☉ yr^-1, placing it at the massive end of the star-forming main sequence at this redshift. The study also confirms 109 galaxies at z = 5.17–5.30 through Hα emission, including eight previously confirmed galaxies. These galaxies are distributed in a filamentary structure, resembling cosmic web filaments seen in simulations. The findings suggest that 50% ± 20% of cosmic star formation at z = 5.1–5.5 occurs in protocluster environments. The paper discusses the implications for the nature of HDF850.1, suggesting it is not necessarily a major merger but could be influenced by minor mergers or secular evolution.The paper presents the resolved stellar component and filamentary overdense environment of the Hubble Space Telescope (HST)-dark submillimeter galaxy HDF850.1 at z = 5.18, observed with the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES). HDF850.1 is known for its heavy dust obscuration and is embedded in an overdense environment. Using nine-band NIRCam images, the authors detect and resolve the rest-frame UV-optical counterpart of HDF850.1 into two components due to dust obscuration in the center. The southern component exhibits significant UV and Hα emission, making the galaxy approximately 100 times above the empirical relation between infrared excess and UV continuum slope. The northern component is more attenuated by dust and thus fainter in UV and Hα. The authors construct a spatially resolved dust-attenuation map, which matches well with millimeter interferometry data. The system hosts a stellar mass of 10^10.8±0.1 M☉ and a star formation rate (SFR) of 10^-8.2±0.5 M☉ yr^-1, placing it at the massive end of the star-forming main sequence at this redshift. The study also confirms 109 galaxies at z = 5.17–5.30 through Hα emission, including eight previously confirmed galaxies. These galaxies are distributed in a filamentary structure, resembling cosmic web filaments seen in simulations. The findings suggest that 50% ± 20% of cosmic star formation at z = 5.1–5.5 occurs in protocluster environments. The paper discusses the implications for the nature of HDF850.1, suggesting it is not necessarily a major merger but could be influenced by minor mergers or secular evolution.