This episode includes depictions of torture and drug use. Please be advised.

November 2nd, 1976, Mexico City.

Dalton Lee looks out at the crowd surging around his taxi. It's the Day of the Dead Festival,

and hundreds are in skeleton masks and costumes and playing maracas or drums.

Others carry flowers and hold lighted candles for the dead.

Lee takes a sniff of cocaine to steal his nerves.

He's on his way to the Soviet embassy and he's not sure of his welcome.

He can't remember much of his last visit.

It's a blur of alcohol and drugs. He remembers a lot of shouting, mostly at him. He arrived in Mexico City yesterday and signalled

for a meeting, but his KGB handlers never showed. Now he's desperate. He has a shipment of heroin

coming due for payment, and he's out of money. But he's desperate. He has a shipment of heroin coming due for payment and he's out of money.

But he's been sitting on some of the spy satellite ciphers and documents provided by his friend

Christopher Boyce for moments just like this.

The taxi drops Lee near the Soviet embassy.

Now he's here, he needs to get past the security guard at the entrance.

He spots a black limo with diplomatic number plates causing the traffic.

It's heading towards the embassy.

He grins and joins the crowd milling on the sidewalk outside the entrance.

The limo inches forward and then turns into the embassy.

As the gates open, Lee crouches down near the back tire of the limo on the opposite side to the security guard.

Staying low, he moves on his haunches using the cover of the car

to sneak inside the walled embassy. He keeps to the shadows

...