  We report on the detection and early characterization of a hot Jupiter in a
3-day orbit around K2-34 (EPIC~212110888), a metal-rich F-type star located in
the K2 Cycle 5 field. Our follow-up campaign involves precise radial velocity
(RV) measurements and high-contrast imaging using multiple facilities. The
absence of a bright nearby source in our high-contrast data suggests that the
transit-like signals are not due to light variations from such a companion
star. Our intensive RV measurements show that K2-34b has a mass of
$1.773\pm0.086M_J$, confirming its status as a planet. We also detect the
Rossiter-McLaughlin effect for K2-34b and show that the system has a good
spin-orbit alignment ($\lambda=-1_{-9}^{+10}$ degrees). High-contrast images
obtained by the HiCIAO camera on the Subaru 8.2-m telescope reveal a faint
companion candidate ($\Delta m_H=6.19\pm 0.11$ mag) at a separation of
$0\farcs36$. Follow-up observations are needed to confirm that the companion
candidate is physically associated with K2-34. K2-34b appears to be an example
of a typical "hot Jupiter," albeit one which can be precisely characterized
using a combination of K2 photometry and ground-based follow-up.
