Disgusted with this treatment, and despising the vices and luxury of Ptolemy, when he did resume command in Coele-Syria (219 BC), Theodotus conceived the idea of passing that province into the hands of Antiochus.
His overtures were readily welcomed, and he surrendered the two important fortresses of Tyre and Ptolemais to the Seleucid monarch, whom he immediately joined with the forces under his command.
Another of Ptolemy's generals, Nicolaus, prevented Theodotus' plans from being fully effected, and he was able to retain a part of the Syrian provinces under the allegiance of Egypt.
In the campaign of 217 BC, Theodotus commanded a body of ten thousand select troops, and just before the Battle of Raphia he demonstrated his daring by penetrating with only two companions into the heart of the Egyptian camp, in order to assassinate Ptolemy himself.
Mistaking the king's tent, Theodotus slew Ptolemy's physician instead, but escaped safely, returning to the Syrian camp.