No need for a plugin, just use twig's slice
filter, combined with the striptags
filter.
I've thrown in the default
filter for good measure, in case the body is empty for some reason.
{{ entry.body|striptags|slice(0,100)|default('Read more') }}...
slice
will simply output the first 100 characters (starting at 0
the first character), including spaces into the template. striptags
ensures that no html tags will be output.