Special puzzle, because of 16 across. Thought it was going to be very difficult when I solved just one clue on first run through, but it became a bit easier after that. Solving time, 23 mins.
* = anagram < = reversed
ACROSS
8 A RA(t) RAT This refers to Noah’s Ark where animals went in pairs and ended up on that mountain (Old Testament).
9 NEGATIVE (Evita gen)<
11 RING O Starr of the Beatles (relevant to 16 across also)
12 GRAN D (T) OUR
13 PRO TESTER
14 LAT(C)H
16 WHEN I’M SIXTY-FOUR Beatles song and I’m sure it’s in here as Quixote is passing that landmark. Best wishes from this blogger. Square as sixty-four is eight times eight. The rest refers to the lyrics of the song.
19 R AT ON(e)
20 CE LEBRATE (a treble)*
23 RU DIMENTS (mindset)*
25 anTIMONy Timon of Athens
26 DO (MINE) ER
27 TEHRAN (another)* less o i.e. loveless
DOWN
1 SAT RAP
2 RAINFOREST (a frontier’s)*
3 MA LONE Molly Malone – Dublin song
4 REP AIR
5 MAN DA (LA)Y
6 L I DO
7 SE (ARCH)ER
10 A Bill GATES
15 THOMAS MORE (home a storm)*
16 WAR BRIDE Cryptic definition
17 IGNOMI NuttY (I’m goin)*
18 XY (LO) SE (sexy)* wood sugar
20 CONTES(t)
21 B (first letter i.e. prime requirement) UTTER (say) & lit
22 EL NINO (online)*
24 DOMEstic