conspired against him, and smote him in Samaria, in the palace of the
king's house;
Josephus ^F2 says it was at a banquet:

with Argob, and Arieh;
whom, according to Abarbinel, Pekah slew with the king, being mighty men, who were always about him; but they seem rather to be conspirators with Pekah, and assisting to him in smiting the king; the former of these, Ben Gersom thinks, was governor of Argob, a country on the other side Jordan, and the latter had his name from his fortitude, which signifies a lion:

and with him fifty men of the Gileadites;
which may seem to strengthen the above notion concerning Argob, since the Gileadites were of the same side of Jordan, and were near Argob, see ( Deuteronomy 3:13 )

and he killed him, and reigned in his room,
as his father killed Shallum, and reigned in his stead.

F1 Ut supra. (Antiqu. l. 9. c. 11. sect. 1.)
F2 Ibid.