Also known as 'Seven Shawls of Yellow Silk' in its native Italian (which is less of a spoilery title), this film was made at the height of the giallo boom, and arguably marks the moment when the filone's characteristics really became formalised. Liberally borrowing from Bava and, especially, Argento's classics, Sergio Pastore has created a film which functions as a sort of greatest hits compilation (albeit a compilation of supermarket-style cover versions) until an abrupt left turn treats us to a finale featuring one of the grisliest set-pieces that's ever been filmed.
I could list the numerous references to Bav and Daz, so I will: fashion house setting (B&BL), blind protagonist (Co9T), musician protagonist (4FoGV) bird sounds on a telephone call pinpointing a location (BwtCP), animal shoehorned into plot/title (all Argento), amateur sleuth who's driven to investigate regardless of the personal toll it exacts (all Argento). Another device which is stolen/borrowed/homaged is the creation of an alibi which seemingly proves the killer's innocence (B&BL). In Bava's film the main killer manufactures a situation whereby they have an ironclad alibi, provided by the police no less, as they're in custody when a murder is committed. Here we swim in slightly muddier waters, with arguably four killers - the blackmailer, who masterminds everything; the blackmailee, who is coerced into transporting the mysterious basket to the site of a couple of the murders; the object in the basket, which commits a couple of the murders; and the blackmailing mastermind's guardian angel, who acts slightly irrationally to protect the blackmailer (/to make us think they're the mastermind and thus set us up for a shocking last second twist). The mastermind actually provides a false alibi for someone which tricks us into cleverly deducing that they're potentially lying in order to hide that someone's guilt, whereas actually they're planting an alibi to mask their own guilt. This is a neat device, which is unfortunately rendered less effective by the multiple murderers (and murdering things in baskets) knocking around, which essentially renders any and all alibis worthless.
The murder device at the heart of the film, which is alluded to by both the English and Italian titles, is among the most ludicrous of the filone. After gifting each victim a yellowy-white shawl, the blackmailee then places a basket containing a cat (yes, that's what's in the box) somewhere nearby. The shawl is dipped in a chemical which attracts (/angers) the cat, and the cat's claws are dipped in curare, a fast-acting paralytic agent which can sometimes lead to death by suffocation or cardiac arrest. The many moving parts of this murder method always manage to line up, but, given the blackmailer isn't above doing their own dirty work by just knifing people to death, employing the cat-poison method is ultimately ludicrously over-engineered. However, a) as stated, there is a bit of a fun-with-alibis vibe at play, which wouldn't be possible if the mastermind was running around knifing everyone themselves, and b) if you wanted realistic and practical murder plots you wouldn't be watching gialli.*
The setting of Copenhagen (and a bit of Germany) is certainly novel, with some decent travelogue footage padding out the Italian-shot interiors. Sergio Pastore's direction is solid, if never coming close to the then-recent heights of Bava and Argento, or even Fulci or Martino. There's an interesting mixture of lengthy, zoom- and rack focus-heavy takes and chaotic, fast-paced sequences which were shot with a more-is-more approach to filming, with lighting, framing and general precision taking a back seat as Pastore, his camerman and the editor cram in as many different angles and takes as possible. He tries to sell the Big Reveal moments - the discovery of corpses etc - by repeating shots (crash zooms) several times, or combining takes (crash zooms) from similar but slightly different angles, as the chaos reaches a(n apparent) thematic and stylistic crescendo. But then, just as you think you've sat through a breezy, fun Argento clone, Pastore throws in one of the most gruesome murder scenes ever filmed.
This scene - the slashing of a showering lady, was filmed only 12 years after Psycho, but it's an unbelievable progression in terms of gore. There's actually a foreshadowing scene in the film - a brief, intense array of close ups of a stabbing which are revealed to be from a scene in a film-within-the-film for which Peter's providing a score. These shots are brutal and graphic, but devoid of context they function as little more than an especially intense scene transition; there's an undeniable sense that what we're witnessing isn't 'real', even within the world of the film. On the contrary, the climactic shower slashing is extremely 'real', and depicts the slaughter of an extremely sympathetic character, who is essentially an unwitting casualty of Peter's obsessive pursuit of the killer. This context, allied to the frenzied editing and general energy of the bloodletting shots, produces an incredibly powerful sequence which is all the more shocking for coming at the tail end of this curare's egg (not a typo; the poison is called 'curare' remember, so it's a clever pun) of a film: it's not top tier, but there are few more gialloey gialli in existence.
*On the other hand, c) there seem to be only 2 murders planned initially, one of which is a cat-in-a-basket kill and one of which is a knifey job committed by the mastermind, who doesn't actually have an alibi for the cat kill, so why didn't they just do both murders themselves and d) it seems unnecessarily risky to involve a blackmailed drug addict in your zany scheme.