They had met on a trip to Ul Qoma, where she had attended a lecture by writer David Bowden, who espouses his theory of the existence of a hidden third city named Orciny.
In Ul Qoma, Borlú discovers that Mahalia was an archaeology student and admirer of Bowden who worked at a dig site where inexplicable artifacts are being found.
Bowden disappears after a mail bomb addressed to him explodes at the dig site, and Borlú realises that people connected to the Orciny theory are being targeted.
Meanwhile, Corwi investigates links between Yorj Syedr, a high-profile nationalist politician in Besźel, and American entrepreneur Mike Gorse, who controls a mega corporation dominating the landscape.
Using Breach's intelligence, they discover that Mahalia stole artifacts from the dig site in Ul Qoma, believing she could gain entry to Orciny by delivering them through the Dissensi.
Retracing her steps, Borlú finds an underground chamber built by Mike Gorse where Syedr's men picked up the stolen artifacts.
He determines that Mahalia was killed by Bowden when she confronted him about promulgating the lie of Orsiny to rope her into the scheme, which she discovered when she followed one of the packages of artifacts she was delivering.
When the American corporate magnate Gorse is confronted with his part in the scheme he boasts he really wanted the artfacts to reengineer the ancient technology of a previously unknown alloy better than any currently available.
Bringing Miéville's setting to the screen presented the challenge of showing two distinct worlds co-existing, and to let the viewer share its inhabitants' point of view.
Besźel resembles the old Eastern Europe of the early 1990s, the streets are filled with communist-era cars and most of the more modern technology such as computers consists of secondhand imports, coloured with soft yellows, greens and browns, while Ul Qoma is described on the DVD "making of" documentary as resembling the new Eastern Europe of the oligarchs, and bright red with blue or blue-white dominate.
Besź is shown as written in English, though with Czech diacritics and some Cyrillic letters, while Illitan was devised for the programme by linguist Dr. Alison Long.
Critical response following the first episode was generally favourable, particularly over the realization of the two cities; Jeff Robson of the i stated it "looks fantastic" and was "equal parts Blade Runner, 1984, and John le Carré at his most downbeat".