Short answers, pulled from the story.
The Novgorod Codex was discovered on the 13th of July 2000 in Veliky Novgorod, Russia, during the Novgorod Archaeological Expedition led by professor Valentin Yanin. It was found buried in the soil beneath a medieval wooden walkway.
The Novgorod Codex is dated to a 42-year window between 988 and 1030 CE, making it the oldest-known book of the Kievan Rus'. Radiocarbon dating of the wax at Uppsala University gave a range of 760-1030 with 95.4% certainty, and the year 999 appears several times in the text itself.
The visible wax surface contains Psalms 75 and 76 and a fragment of Psalm 67. Hidden scratches beneath the wax preserve dozens of concealed texts, including psalms, the beginning of the Apocalypse of John, a previously-unattested Old Church Slavonic translation of John Chrysostom's treatise On virginity, and several previously-unknown texts attributed to a figure named Alexander of Laodicea.
Linguist Andrey Zaliznyak concluded that the scribe was the monk Isaakiy, who in 999 CE was posted as a priest in Suzdal. Isaakiy was a follower of a self-proclaimed prophet named Alexander, an Armenian who taught from Thracia and whose doctrine Zaliznyak connected to an early form of Bogomilism.
Andrey Zaliznyak coined the term hyper-palimpsest to describe the concealed layer of the Novgorod Codex. Tens of thousands of letter traces left by a stylus over decades are superimposed on each other in the soft lime wood beneath the wax, making reconstruction of individual texts a process that can take weeks per page.
The codex uses a monoyeric orthography, writing only the letter ъ where standard Old Church Slavonic used two yer letters, ь and ъ. Before the codex's discovery, scholars believed the dual-yer system was original and the single-yer system was a later development; the codex proved the reverse was true.