the author inadvertently reveals the murderer in the penultimate chapter.
Examples of penultimate
penultimate
This was the ninth and penultimate check-up before the Games begin in July 2012.
From the independent.co.uk
By directing us to the ultimate, religion defines the limits of the penultimate.
From the stltoday.com
We were riding Stage 7, the penultimate stage in this year's Tour of California.
From the suntimes.com
It is the penultimate expedition in the shuttle's history, and Endeavour's last.
From the guardian.co.uk
At the moment, I find myself in the penultimate stage on President Barack Obama.
From the post-gazette.com
The game was a marquee matchup in the penultimate contest of the regular season.
From the newsday.com
The team Astana rider made his move at the foot of stage 19's penultimate climb.
From the independent.co.uk
Mr Wolfensohn was speaking on March 21st, the penultimate day of the conference.
From the economist.com
The sole sour note came on the penultimate day of action, the men's 4x400m relay.
From the thisislondon.co.uk
More examples
Next to the last; "the author inadvertently reveals the murderer in the penultimate chapter"; "the figures in the next-to-last column"
Penult: the next to last syllable in a word
Next to last; one molt shy of adulthood. The genitalia are partially formed and slightly visible. In males, the tips of the palps are smooth and swollen like boxing gloves. In females, there is a hardened and sometimes darkened area where the epigynum will soon be.
The last and largest number in the series of countable numbers. Where Infinity once was, the Penultimate is now just before. Penultimate is denoted as P, not to be confused with p of propositional logic. ...
This is the second to last hoop in a complete game.
Literally, next to last. I have used it with reference to a political right that gives way to one other right that can supersede it (that is, Roe v. Wade). Antepenultimate would refer to a right that gives way to two other rights (a rather disturbing thought experiment, to be sure). ...