When several unexplained deaths occur in a retirement village, a cranky veteran suspects the widows and must uncover the truth before becoming the next to go.

Rearrange the details for better flow. I don't know who ever said starting a logline with "When something happens" but it's terrible and doesn't make sense that so many people use it without listening to how slow and boring it sounds.

Always start with the protagonist - no one cares about events, we care about people. Aside from how it's phrased, all the pertinent details are here: protagonist, antagonist, conflict, stakes. Just put it in a more compelling order without punctuation and it's solid.

A cranky veteran must uncover the truth behind several unexplained deaths in his retirement village before the widowed suspects make him the next to go.

This doesn't quite identify the tone - could be dark comedy, could be dramatic thriller - but does generate interest in reading more, so as long as the tone is clear in a synopsis or summary or treatment or especially the script, it's fine.

I like the idea? of romancing the suspects, but suggest focusing on a plot involving romancing the prime suspect..? Focus on one woman and the relationship that develops in spite of his suspicions.

So something like:

After several mysterious deaths in a retirement community, a retired detective romances the prime suspect to solve the case.

The plot twist/complication is he falls in love with her.? What should he trust, his heart or his head?

I like the idea? of romancing the suspects, but suggest focusing on a plot involving romancing the prime suspect..? Focus on one woman and the relationship that develops in spite of his suspicions.

So something like:

After several mysterious deaths in a retirement community, a retired detective romances the prime suspect to solve the case.

The plot twist/complication is he falls in love with her.? What should he trust, his heart or his head?