  We investigate the performance of T2HK in the presence of a light eV scale
sterile neutrino. We study in detail its influence in resolving fundamental
issues like mass hierarchy, CP-violation (CPV) induced by the standard CP-phase
$\delta_{13}$ and new CP-phase $\delta_{14}$, and the octant ambiguity of
$\theta_{23}$. We show for the first time in detail that due to the impressive
energy reconstruction capabilities of T2HK, the available spectral information
plays an important role to enhance the mass hierarchy discovery reach of this
experiment in 3$\nu$ framework and also to keep it almost intact even in $4\nu$
scheme. This feature is also of the utmost importance in establishing the CPV
due to $\delta_{14}$. As far as the sensitivity to CPV due to $\delta_{13}$ is
concerned, it does not change much going from $3\nu$ to 4$\nu$ case. We also
examine the reconstruction capability of the two phases $\delta_{13}$ and
$\delta_{14}$, and find that the typical 1$\sigma$ uncertainty on $\delta_{13}$
($\delta_{14}$) in T2HK is $\sim15^0$ ($30^0$). While determining the octant of
$\theta_{23}$, we face a complete loss of sensitivity for unfavorable
combinations of unknown $\delta_{13}$ and $\delta_{14}$.
