Durell got his orders from McFee, Chief of K Section of the CIA.

"This time," McFee told Durell, "it's really hot, Sam. All signals are red - everywhere."
"And it's up to me - ."
"It's up to you. Find that underground railroad or whatever it is that the best agents in the world can't trace. Find it, buy a ticket on it, and ride it to its final destination."
Durell said "They might not let me in the station, so to speak."
"I don't care how you get aboard, Sam, but you must find the other terminal. Be a decoy. Play it dumb. Blunder about a bit." McFee looked haunted. "Of course, Sam, you could get killed..."