TV top picks
6 p.m. on TNT The Librarians
The Season 4 finale, “And the Echoes of Memory,” opens with the world transformed into a dystopian nightmare where the Library never existed. Surveying the horrors around her, Baird (Rebecca Romijn) knows the only way to stop this chain of events is to reunite the Librarians (Christian Kane, Lindy Booth, John Harlan Kim) before this bleak world imprints itself and becomes their permanent reality.
7 p.m. on CBS Big Brother: Celebrity Edition
Celebrity editions of the competition have been staged in foreign versions, but never in the American one ... until now. Familiar faces including Omarosa Manigault, singeractor Mark McGrath, Keshia Knight Pulliam and Ross Mathews become housemates in this new round, which will play out on multiple nights over several weeks instead of all summer. All of the show’s usual elements will be present, including Head of Household contests and evictions — and Julie Chen, pictured, as host.
7 p.m. on TRAV Expedition Unknown
In the first of an epic two-part special called “Great Women of Ancient Egypt,” host and adventurer Josh Gates reveals the stories of three of the most powerful yet elusive women of that long-vanished world of yore: Cleopatra, Nefertiti and Hatshepsut, the second historically confirmed female pharaoh. Even though eons have passed since this trio were alive, it seems bizarre that so very little is known of these once-mighty females. Gates travels to the land of the Nile in search of answers. 9-1-1 Even if it’s a week early, a Valentine’s Day-themed episode still is timely with the new tale “Heartbreaker.” An unexpected proposal takes a dangerous turn that requires the assistance of first responders, while Athena (Angela Bassett) ends up becoming a member of a club for single people. Abby and Buck (Connie Britton, Oliver Stark) have their first date. Mariette Hartley continues her recurring guest role. Impossible Builds Buildings that are at least improbable — if not downright impossible — in their unusual construction are showcased in this new threepart series, which starts with “The Scorpion Tower,” profiling a Miami building that has its skeleton placed externally and the supporting columns on the inside. Largely devised in Dubai and shipped in pieces to America for assembly, the 700-foottall project was set back slightly by the death of architect Zaha Hadid.