The most common and most likely answer to this crossword clue is the 8 letter word IMMERSES
I've seen this crossword clue in Independent
I
M
M
E
R
S
E
S
Buddy explains!
The straight part
We know that "Is riveting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case is riveting = immerses.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does IMMERSES mean?
IMMERSES verb- To put under the surface of a liquid; to dunk.
- To involve or engage deeply.
- To map into an immersion.