  High-spin states of neutron deficient Trans-Lead nucleus $^{204}$At were
populated up to $\sim 8\,{\rm MeV}$ excitation through the $^{12}$C +
$^{197}$Au fusion evaporation reaction. Decay of the associated levels through
prompt and delayed $\gamma$-ray emissions were studied to evaluate the
underlying nuclear structure. The level scheme, which was partly known, was
extended further. An isomeric $16^+$ level with observed lifetime $\tau=52 \pm
5\, {\rm ns}$, was established from our measurements. Attempts were made to
interpret the excited states based on multi quasiparticle and hole structures
involving $2f_{5/2}$, $1h_{9/2}$, and $1i_{13/2}$ shell model states, along
with moderate core excitation. Magnetic dipole band structure over the spin
parity range:~$16^+ - 23^+$ was confirmed and evaluated in more detail,
including the missing cross-over $E2$ transitions. Band-crossing along the
shears band was observed and compared with the evidence of similar phenomena in
the neighbouring neutron deficient $^{202}$Bi, $^{205}$Rn isotones and the
$^{203}$At isotope. Based on comparison of the measured $B(M1)/B(E2)$ values
for transitions along the band with the semiclassical model based estimates,
the shears band of $^{204}$At was established along with the level scheme.
