Put the meaning into your own words.

The detective rejected the implausible explanation for the missing statue.

After three successful pop-up exhibitions, the organizers grew complacent and stopped checking whether their usual room was available. Their confidence rested on flimsy evidence: an unsigned message saying that the date looked fine. When another group produced a confirmed booking, one organizer offered an implausible explanation that both groups somehow had exclusive use of the same room at the same time.